---
layout: docs
page_title: Configuration
sidebar_title: Configuration
description: >-
  The agent has various configuration options that can be specified via the
  command-line or via configuration files. All of the configuration options are
  completely optional. Defaults are specified with their descriptions.
---

# Configuration

The agent has various configuration options that can be specified via
the command-line or via configuration files. All of the configuration
options are completely optional. Defaults are specified with their
descriptions.

Configuration precedence is evaluated in the following order:

1. Command line arguments
2. Configuration files

When loading configuration, Consul loads the configuration from files and
directories in lexical order. For example, configuration file
`basic_config.json` will be processed before `extra_config.json`. Configuration
can be in either [HCL](https://github.com/hashicorp/hcl#syntax) or JSON format.
Available in Consul 1.0 and later, the HCL support now requires an `.hcl` or
`.json` extension on all configuration files in order to specify their format.

Configuration specified later will be merged into configuration specified
earlier. In most cases, "merge" means that the later version will override the
earlier. In some cases, such as event handlers, merging appends the handlers to
the existing configuration. The exact merging behavior is specified for each
option below.

Consul also supports reloading configuration when it receives the
SIGHUP signal. Not all changes are respected, but those that are
documented below in the
[Reloadable Configuration](#reloadable-configuration) section. The
[reload command](/docs/commands/reload) can also be used to trigger a
configuration reload.

You can test the following configuration options by following the
[Getting Started](https://learn.hashicorp.com/tutorials/consul/get-started-install?utm_source=consul.io&utm_medium=docs)
tutorials to install a local agent.

## Environment Variables

Environment variables **cannot** be used to configure the Consul client. They
_can_ be used when running other `consul` CLI commands that connect with a
running agent, e.g. `CONSUL_HTTP_ADDR=192.168.0.1:8500 consul members`.

See [Consul Commands](/docs/commands#environment-variables) for more
information.

## Command-line Options ((#commandline_options))

The options below are all specified on the command-line.

- `-advertise` ((#\_advertise)) - The advertise address is used to change
  the address that we advertise to other nodes in the cluster. By default, the [`-bind`](#_bind)
  address is advertised. However, in some cases, there may be a routable address
  that cannot be bound. This flag enables gossiping a different address to support
  this. If this address is not routable, the node will be in a constant flapping
  state as other nodes will treat the non-routability as a failure. In Consul 1.0
  and later this can be set to a [go-sockaddr](https://godoc.org/github.com/hashicorp/go-sockaddr/template)
  template.

- `-advertise-wan` ((#\_advertise-wan)) - The advertise WAN address is used
  to change the address that we advertise to server nodes joining through the WAN.
  This can also be set on client agents when used in combination with the [`translate_wan_addrs`](#translate_wan_addrs) configuration option. By default, the [`-advertise`](#_advertise) address
  is advertised. However, in some cases all members of all datacenters cannot be
  on the same physical or virtual network, especially on hybrid setups mixing cloud
  and private datacenters. This flag enables server nodes gossiping through the public
  network for the WAN while using private VLANs for gossiping to each other and their
  client agents, and it allows client agents to be reached at this address when being
  accessed from a remote datacenter if the remote datacenter is configured with [`translate_wan_addrs`](#translate_wan_addrs). In Consul 1.0 and later this can be set to a [go-sockaddr](https://godoc.org/github.com/hashicorp/go-sockaddr/template) template

- `-bootstrap` ((#\_bootstrap)) - This flag is used to control if a server
  is in "bootstrap" mode. It is important that no more than one server **per** datacenter
  be running in this mode. Technically, a server in bootstrap mode is allowed to
  self-elect as the Raft leader. It is important that only a single node is in this
  mode; otherwise, consistency cannot be guaranteed as multiple nodes are able to
  self-elect. It is not recommended to use this flag after a cluster has been bootstrapped.

- `-bootstrap-expect` ((#\_bootstrap_expect)) - This flag provides the number
  of expected servers in the datacenter. Either this value should not be provided
  or the value must agree with other servers in the cluster. When provided, Consul
  waits until the specified number of servers are available and then bootstraps the
  cluster. This allows an initial leader to be elected automatically. This cannot
  be used in conjunction with the legacy [`-bootstrap`](#_bootstrap) flag. This flag
  requires [`-server`](#_server) mode.

- `-bind` ((#\_bind)) - The address that should be bound to for internal
  cluster communications. This is an IP address that should be reachable by all other
  nodes in the cluster. By default, this is "0.0.0.0", meaning Consul will bind to
  all addresses on the local machine and will [advertise](/docs/agent/options#_advertise)
  the private IPv4 address to the rest of the cluster. If there are multiple private
  IPv4 addresses available, Consul will exit with an error at startup. If you specify
  `"[::]"`, Consul will [advertise](/docs/agent/options#_advertise) the public
  IPv6 address. If there are multiple public IPv6 addresses available, Consul will
  exit with an error at startup. Consul uses both TCP and UDP and the same port for
  both. If you have any firewalls, be sure to allow both protocols. In Consul 1.0
  and later this can be set to a [go-sockaddr](https://godoc.org/github.com/hashicorp/go-sockaddr/template)
  template that needs to resolve to a single address. Some example templates:

  ```shell
  # Using address within a specific CIDR
  $ consul agent -bind '{{ GetPrivateInterfaces | include "network" "10.0.0.0/8" | attr "address" }}'
  ```

  ```shell
  # Using a static network interface name
  $ consul agent -bind '{{ GetInterfaceIP "eth0" }}'
  ```

  ```shell
  # Using regular expression matching for network interface name that is forwardable and up
  $ consul agent -bind '{{ GetAllInterfaces | include "name" "^eth" | include "flags" "forwardable|up" | attr "address" }}'
  ```

- `-serf-wan-bind` ((#\_serf_wan_bind)) - The address that should be bound
  to for Serf WAN gossip communications. By default, the value follows the same rules
  as [`-bind` command-line flag](#_bind), and if this is not specified, the `-bind`
  option is used. This is available in Consul 0.7.1 and later. In Consul 1.0 and
  later this can be set to a [go-sockaddr](https://godoc.org/github.com/hashicorp/go-sockaddr/template)
  template

- `-serf-lan-bind` ((#\_serf_lan_bind)) - The address that should be bound
  to for Serf LAN gossip communications. This is an IP address that should be reachable
  by all other LAN nodes in the cluster. By default, the value follows the same rules
  as [`-bind` command-line flag](#_bind), and if this is not specified, the `-bind`
  option is used. This is available in Consul 0.7.1 and later. In Consul 1.0 and
  later this can be set to a [go-sockaddr](https://godoc.org/github.com/hashicorp/go-sockaddr/template)
  template

- `-check_output_max_size` - Override the default
  limit of 4k for maximum size of checks, this is a positive value. By limiting this
  size, it allows to put less pressure on Consul servers when many checks are having
  a very large output in their checks. In order to completely disable check output
  capture, it is possible to use [`discard_check_output`](#discard_check_output).

- `-client` ((#\_client)) - The address to which Consul will bind client
  interfaces, including the HTTP and DNS servers. By default, this is "127.0.0.1",
  allowing only loopback connections. In Consul 1.0 and later this can be set to
  a space-separated list of addresses to bind to, or a [go-sockaddr](https://godoc.org/github.com/hashicorp/go-sockaddr/template)
  template that can potentially resolve to multiple addresses.

- `-config-file` ((#\_config_file)) - A configuration file to load. For
  more information on the format of this file, read the [Configuration Files](#configuration_files)
  section. This option can be specified multiple times to load multiple configuration
  files. If it is specified multiple times, configuration files loaded later will
  merge with configuration files loaded earlier. During a config merge, single-value
  keys (string, int, bool) will simply have their values replaced while list types
  will be appended together.

- `-config-dir` ((#\_config_dir)) - A directory of configuration files to
  load. Consul will load all files in this directory with the suffix ".json" or ".hcl".
  The load order is alphabetical, and the the same merge routine is used as with
  the [`config-file`](#_config_file) option above. This option can be specified multiple
  times to load multiple directories. Sub-directories of the config directory are
  not loaded. For more information on the format of the configuration files, see
  the [Configuration Files](#configuration_files) section.

- `-config-format` ((#\_config_format)) - The format of the configuration
  files to load. Normally, Consul detects the format of the config files from the
  ".json" or ".hcl" extension. Setting this option to either "json" or "hcl" forces
  Consul to interpret any file with or without extension to be interpreted in that
  format.

- `-data-dir` ((#\_data_dir)) - This flag provides a data directory for
  the agent to store state. This is required for all agents. The directory should
  be durable across reboots. This is especially critical for agents that are running
  in server mode as they must be able to persist cluster state. Additionally, the
  directory must support the use of filesystem locking, meaning some types of mounted
  folders (e.g. VirtualBox shared folders) may not be suitable.

  **Note:** both server and non-server agents may store ACL tokens in the state in this directory so read access may grant access to any tokens on servers and to any tokens used during service registration on non-servers. On Unix-based platforms the files are written with 0600 permissions so you should ensure only trusted processes can execute as the same user as Consul. On Windows, you should ensure the directory has suitable permissions configured as these will be inherited.

- `-datacenter` ((#\_datacenter)) - This flag controls the datacenter in
  which the agent is running. If not provided, it defaults to "dc1". Consul has first-class
  support for multiple datacenters, but it relies on proper configuration. Nodes
  in the same datacenter should be on a single LAN.

- `-dev` ((#\_dev)) - Enable development server mode. This is useful for
  quickly starting a Consul agent with all persistence options turned off, enabling
  an in-memory server which can be used for rapid prototyping or developing against
  the API. In this mode, [Connect is enabled](/docs/connect/configuration) and
  will by default create a new root CA certificate on startup. This mode is **not**
  intended for production use as it does not write any data to disk. The gRPC port
  is also defaulted to `8502` in this mode.

- `-disable-host-node-id` ((#\_disable_host_node_id)) - Setting this to
  true will prevent Consul from using information from the host to generate a deterministic
  node ID, and will instead generate a random node ID which will be persisted in
  the data directory. This is useful when running multiple Consul agents on the same
  host for testing. This defaults to false in Consul prior to version 0.8.5 and in
  0.8.5 and later defaults to true, so you must opt-in for host-based IDs. Host-based
  IDs are generated using [gopsutil](https://github.com/shirou/gopsutil/tree/master/host), which
  is shared with HashiCorp's [Nomad](https://www.nomadproject.io/), so if you opt-in
  to host-based IDs then Consul and Nomad will use information on the host to automatically
  assign the same ID in both systems.

- `-disable-keyring-file` ((#\_disable_keyring_file)) - If set, the keyring
  will not be persisted to a file. Any installed keys will be lost on shutdown, and
  only the given `-encrypt` key will be available on startup. This defaults to false.

- `-dns-port` ((#\_dns_port)) - the DNS port to listen on. This overrides
  the default port 8600. This is available in Consul 0.7 and later.

- `-domain` ((#\_domain)) - By default, Consul responds to DNS queries in
  the "consul." domain. This flag can be used to change that domain. All queries
  in this domain are assumed to be handled by Consul and will not be recursively
  resolved.

- `-alt-domain` ((#\_alt_domain)) - This flag allows Consul to respond to
  DNS queries in an alternate domain, in addition to the primary domain. If unset,
  no alternate domain is used.

- `-enable-script-checks` ((#\_enable_script_checks)) This controls whether
  [health checks that execute scripts](/docs/agent/checks) are enabled on this
  agent, and defaults to `false` so operators must opt-in to allowing these. This
  was added in Consul 0.9.0.

  ~> **Security Warning:** Enabling script checks in some configurations may
  introduce a remote execution vulnerability which is known to be targeted by
  malware. We strongly recommend `-enable-local-script-checks` instead. See [this
  blog post](https://www.hashicorp.com/blog/protecting-consul-from-rce-risk-in-specific-configurations)
  for more details.

- `-enable-local-script-checks` ((#\_enable_local_script_checks))
  Like [`enable_script_checks`](#_enable_script_checks), but only enable them when
  they are defined in the local configuration files. Script checks defined in HTTP
  API registrations will still not be allowed.

- `-encrypt` ((#\_encrypt)) - Specifies the secret key to use for encryption
  of Consul network traffic. This key must be 32-bytes that are Base64-encoded. The
  easiest way to create an encryption key is to use [`consul keygen`](/docs/commands/keygen).
  All nodes within a cluster must share the same encryption key to communicate. The
  provided key is automatically persisted to the data directory and loaded automatically
  whenever the agent is restarted. This means that to encrypt Consul's gossip protocol,
  this option only needs to be provided once on each agent's initial startup sequence.
  If it is provided after Consul has been initialized with an encryption key, then
  the provided key is ignored and a warning will be displayed.

- `-grpc-port` ((#\_grpc_port)) - the gRPC API port to listen on. Default
  -1 (gRPC disabled). See [ports](#ports) documentation for more detail.

- `-hcl` ((#\_hcl)) - A HCL configuration fragment. This HCL configuration
  fragment is appended to the configuration and allows to specify the full range
  of options of a config file on the command line. This option can be specified multiple
  times. This was added in Consul 1.0.

- `-http-port` ((#\_http_port)) - the HTTP API port to listen on. This overrides
  the default port 8500. This option is very useful when deploying Consul to an environment
  which communicates the HTTP port through the environment e.g. PaaS like CloudFoundry,
  allowing you to set the port directly via a Procfile.

- `-https-port` ((#\_https_port)) - the HTTPS API port to listen on. Default
  -1 (https disabled). See [ports](#ports) documentation for more detail.

- `-log-file` ((#\_log_file)) - writes all the Consul agent log messages
  to a file. This value is used as a prefix for the log file name. The current timestamp
  is appended to the file name. If the value ends in a path separator, `consul-`
  will be appened to the value. If the file name is missing an extension, `.log`
  is appended. For example, setting `log-file` to `/var/log/` would result in a log
  file path of `/var/log/consul-{timestamp}.log`. `log-file` can be combined with
  [`-log-rotate-bytes`](#_log_rotate_bytes) and [-log-rotate-duration](#_log_rotate_duration)
  for a fine-grained log rotation experience.

- `-log-rotate-bytes` ((#\_log_rotate_bytes)) - to specify the number of
  bytes that should be written to a log before it needs to be rotated. Unless specified,
  there is no limit to the number of bytes that can be written to a log file.

- `-log-rotate-duration` ((#\_log_rotate_duration)) - to specify the maximum
  duration a log should be written to before it needs to be rotated. Must be a duration
  value such as 30s. Defaults to 24h.

- `-log-rotate-max-files` ((#\_log_rotate_max_files)) - to specify the maximum
  number of older log file archives to keep. Defaults to 0 (no files are ever deleted).
  Set to -1 to discard old log files when a new one is created.

- `-default-query-time` ((#\_default_query_time)) - This flag controls the
  amount of time a blocking query will wait before Consul will force a response.
  This value can be overridden by the `wait` query parameter. Note that Consul applies
  some jitter on top of this time. Defaults to 300s.

- `-max-query-time` ((#\_max_query_time)) - this flag controls the maximum
  amount of time a blocking query can wait before Consul will force a response. Consul
  applies jitter to the wait time. The jittered time will be capped to this time.
  Defaults to 600s.

- `-join` ((#\_join)) - Address of another agent to join upon starting up.
  This can be specified multiple times to specify multiple agents to join. If Consul
  is unable to join with any of the specified addresses, agent startup will fail.
  By default, the agent won't join any nodes when it starts up. Note that using [`retry_join`](#retry_join) could be more appropriate to help mitigate node startup race conditions when automating
  a Consul cluster deployment.

  In Consul 1.1.0 and later this can be set to a
  [go-sockaddr](https://godoc.org/github.com/hashicorp/go-sockaddr/template)
  template

- `-retry-join` ((#\_retry_join)) - Similar to [`-join`](#_join) but allows retrying a join until
  it is successful. Once it joins successfully to a member in a list of members
  it will never attempt to join again. Agents will then solely maintain their
  membership via gossip. This is useful for cases where you know the address will
  eventually be available. This option can be specified multiple times to
  specify multiple agents to join. The value can contain IPv4, IPv6, or DNS
  addresses. In Consul 1.1.0 and later this can be set to a
  [go-sockaddr](https://godoc.org/github.com/hashicorp/go-sockaddr/template)
  template. If Consul is running on the non-default Serf LAN port, this must be
  specified as well. IPv6 must use the "bracketed" syntax. If multiple values
  are given, they are tried and retried in the order listed until the first
  succeeds. Here are some examples:

  ```shell
  # Using a DNS entry
  $ consul agent -retry-join "consul.domain.internal"
  ```

  ```shell
  # Using IPv4
  $ consul agent -retry-join "10.0.4.67"
  ```

  ```shell
  # Using IPv6
  $ consul agent -retry-join "[::1]:8301"
  ```

  ```shell
  # Using multiple addresses
  $ consul agent -retry-join "consul.domain.internal" -retry-join "10.0.4.67"
  ```

  ### Cloud Auto-Joining

  As of Consul 0.9.1, `retry-join` accepts a unified interface using the
  [go-discover](https://github.com/hashicorp/go-discover) library for doing
  automatic cluster joining using cloud metadata. For more information, see
  the [Cloud Auto-join page](/docs/agent/cloud-auto-join).

  ```shell
  # Using Cloud Auto-Joining
  $ consul agent -retry-join "provider=aws tag_key=..."
  ```

- `-retry-interval` ((#\_retry_interval)) - Time to wait between join attempts.
  Defaults to 30s.

- `-retry-max` ((#\_retry_max)) - The maximum number of [`-join`](#_join)
  attempts to be made before exiting with return code 1. By default, this is set
  to 0 which is interpreted as infinite retries.

- `-join-wan` ((#\_join_wan)) - Address of another wan agent to join upon
  starting up. This can be specified multiple times to specify multiple WAN agents
  to join. If Consul is unable to join with any of the specified addresses, agent
  startup will fail. By default, the agent won't [`-join-wan`](#_join_wan) any nodes
  when it starts up.

  In Consul 1.1.0 and later this can be set to a
  [go-sockaddr](https://godoc.org/github.com/hashicorp/go-sockaddr/template)
  template.

- `-retry-join-wan` ((#\_retry_join_wan)) - Similar to [`retry-join`](#_retry_join)
  but allows retrying a wan join if the first attempt fails. This is useful for cases
  where we know the address will become available eventually. As of Consul 0.9.3
  [Cloud Auto-Joining](#cloud-auto-joining) is supported as well.

  In Consul 1.1.0 and later this can be set to a
  [go-sockaddr](https://godoc.org/github.com/hashicorp/go-sockaddr/template)
  template

- `-retry-interval-wan` ((#\_retry_interval_wan)) - Time to wait between
  [`-join-wan`](#_join_wan) attempts. Defaults to 30s.

- `-retry-max-wan` ((#\_retry_max_wan)) - The maximum number of [`-join-wan`](#_join_wan)
  attempts to be made before exiting with return code 1. By default, this is set
  to 0 which is interpreted as infinite retries.

- `-log-level` ((#\_log_level)) - The level of logging to show after the
  Consul agent has started. This defaults to "info". The available log levels are
  "trace", "debug", "info", "warn", and "err". You can always connect to an agent
  via [`consul monitor`](/docs/commands/monitor) and use any log level. Also,
  the log level can be changed during a config reload.

- `-log-json` ((#\_log_json)) - This flag enables the agent to output logs
  in a JSON format. By default this is false.

- `-node` ((#\_node)) - The name of this node in the cluster. This must
  be unique within the cluster. By default this is the hostname of the machine.

- `-node-id` ((#\_node_id)) - Available in Consul 0.7.3 and later, this
  is a unique identifier for this node across all time, even if the name of the node
  or address changes. This must be in the form of a hex string, 36 characters long,
  such as `adf4238a-882b-9ddc-4a9d-5b6758e4159e`. If this isn't supplied, which is
  the most common case, then the agent will generate an identifier at startup and
  persist it in the [data directory](#_data_dir) so that it will remain the same
  across agent restarts. Information from the host will be used to generate a deterministic
  node ID if possible, unless [`-disable-host-node-id`](#_disable_host_node_id) is
  set to true.

- `-node-meta` ((#\_node_meta)) - Available in Consul 0.7.3 and later, this
  specifies an arbitrary metadata key/value pair to associate with the node, of the
  form `key:value`. This can be specified multiple times. Node metadata pairs have
  the following restrictions:

  - A maximum of 64 key/value pairs can be registered per node.
  - Metadata keys must be between 1 and 128 characters (inclusive) in length
  - Metadata keys must contain only alphanumeric, `-`, and `_` characters.
  - Metadata keys must not begin with the `consul-` prefix; that is reserved for internal use by Consul.
  - Metadata values must be between 0 and 512 (inclusive) characters in length.
  - Metadata values for keys beginning with `rfc1035-` are encoded verbatim in DNS TXT requests, otherwise
    the metadata kv-pair is encoded according [RFC1464](https://www.ietf.org/rfc/rfc1464.txt).

- `-pid-file` ((#\_pid_file)) - This flag provides the file path for the
  agent to store its PID. This is useful for sending signals (for example, `SIGINT`
  to close the agent or `SIGHUP` to update check definitions) to the agent.

- `-protocol` ((#\_protocol)) - The Consul protocol version to use. Consul
  agents speak protocol 2 by default, however agents will automatically use protocol > 2 when speaking to compatible agents. This should be set only when [upgrading](/docs/upgrading). You can view the protocol versions supported by Consul by running `consul -v`.

- `-primary-gateway` ((#\_primary_gateway)) - Similar to [`retry-join-wan`](#_retry_join_wan)
  but allows retrying discovery of fallback addresses for the mesh gateways in the
  primary datacenter if the first attempt fails. This is useful for cases where we
  know the address will become available eventually. [Cloud Auto-Joining](#cloud-auto-joining)
  is supported as well as [go-sockaddr](https://godoc.org/github.com/hashicorp/go-sockaddr/template)
  templates. This was added in Consul 1.8.0.

- `-raft-protocol` ((#\_raft_protocol)) - This controls the internal version
  of the Raft consensus protocol used for server communications. This must be set
  to 3 in order to gain access to Autopilot features, with the exception of [`cleanup_dead_servers`](#cleanup_dead_servers). Defaults to 3 in Consul 1.0.0 and later (defaulted to 2 previously). See [Raft Protocol Version Compatibility](/docs/upgrade-specific#raft-protocol-version-compatibility) for more details.

- `-recursor` ((#\_recursor)) - Specifies the address of an upstream DNS
  server. This option may be provided multiple times, and is functionally equivalent
  to the [`recursors` configuration option](#recursors).

- `-rejoin` ((#\_rejoin)) - When provided, Consul will ignore a previous
  leave and attempt to rejoin the cluster when starting. By default, Consul treats
  leave as a permanent intent and does not attempt to join the cluster again when
  starting. This flag allows the previous state to be used to rejoin the cluster.

- `-segment` ((#\_segment)) <EnterpriseAlert inline /> - This flag is used to set
  the name of the network segment the agent belongs to. An agent can only join and
  communicate with other agents within its network segment. Review the [Network Segments
  tutorial](https://learn.hashicorp.com/tutorials/consul/network-partition-datacenters) for
  more details. By default, this is an empty string, which is the default network
  segment.

- `-serf-lan-allowed-cidrs` ((#\_serf_lan_allowed_cidrs)) - The Serf LAN allowed CIDRs allow to accept incoming
  connections for Serf only from several networks (mutiple values are supported).
  Those networks are specified with CIDR notation (eg: 192.168.1.0/24).
  This is available in Consul 1.8 and later.

- `-serf-lan-port` ((#\_serf_lan_port)) - the Serf LAN port to listen on.
  This overrides the default Serf LAN port 8301. This is available in Consul 1.2.2
  and later.

- `-serf-wan-allowed-cidrs` ((#\_serf_wan_allowed_cidrs)) - The Serf WAN allowed CIDRs allow to accept incoming
  connections for Serf only from several networks (mutiple values are supported).
  Those networks are specified with CIDR notation (eg: 192.168.1.0/24).
  This is available in Consul 1.8 and later.

- `-serf-wan-port` ((#\_serf_wan_port)) - the Serf WAN port to listen on.
  This overrides the default Serf WAN port 8302. This is available in Consul 1.2.2
  and later.

- `-server` ((#\_server)) - This flag is used to control if an agent is
  in server or client mode. When provided, an agent will act as a Consul server.
  Each Consul cluster must have at least one server and ideally no more than 5 per
  datacenter. All servers participate in the Raft consensus algorithm to ensure that
  transactions occur in a consistent, linearizable manner. Transactions modify cluster
  state, which is maintained on all server nodes to ensure availability in the case
  of node failure. Server nodes also participate in a WAN gossip pool with server
  nodes in other datacenters. Servers act as gateways to other datacenters and forward
  traffic as appropriate.

- `-server-port` ((#\_server_port)) - the server RPC port to listen on.
  This overrides the default server RPC port 8300. This is available in Consul 1.2.2
  and later.

- `-non-voting-server` ((#\_non_voting_server)) <EnterpriseAlert inline /> - This
  flag is used to make the server not participate in the Raft quorum, and have it
  only receive the data replication stream. This can be used to add read scalability
  to a cluster in cases where a high volume of reads to servers are needed.

- `-syslog` ((#\_syslog)) - This flag enables logging to syslog. This is
  only supported on Linux and OSX. It will result in an error if provided on Windows.

- `-ui` ((#\_ui)) - Enables the built-in web UI server and the required
  HTTP routes. This eliminates the need to maintain the Consul web UI files separately
  from the binary.

- `-ui-dir` ((#\_ui_dir)) - This flag provides the directory containing
  the Web UI resources for Consul. This will automatically enable the Web UI. The
  directory must be readable to the agent. Starting with Consul version 0.7.0 and
  later, the Web UI assets are included in the binary so this flag is no longer necessary;
  specifying only the `-ui` flag is enough to enable the Web UI. Specifying both
  the '-ui' and '-ui-dir' flags will result in an error.

<!-- prettier-ignore -->
- `-ui-content-path` ((#\_ui\_content\_path)) - This flag provides the option
  to change the path the Consul UI loads from and will be displayed in the browser.
  By default, the path is `/ui/`, for example `http://localhost:8500/ui/`. Only alphanumerics,
  `-`, and `_` are allowed in a custom path.`/v1/` is not allowed as it would overwrite
  the API endpoint.

## Configuration Files ((#configuration_files))

In addition to the command-line options, configuration can be put into
files. This may be easier in certain situations, for example when Consul is
being configured using a configuration management system.

The configuration files are JSON formatted, making them easily readable
and editable by both humans and computers. The configuration is formatted
as a single JSON object with configuration within it.

Configuration files are used for more than just setting up the agent,
they are also used to provide check and service definitions. These are used
to announce the availability of system servers to the rest of the cluster.
They are documented separately under [check configuration](/docs/agent/checks) and
[service configuration](/docs/agent/services) respectively. The service and check
definitions support being updated during a reload.

#### Example Configuration File

```javascript
{
  "datacenter": "east-aws",
  "data_dir": "/opt/consul",
  "log_level": "INFO",
  "node_name": "foobar",
  "server": true,
  "watches": [
    {
        "type": "checks",
        "handler": "/usr/bin/health-check-handler.sh"
    }
  ],
  "telemetry": {
     "statsite_address": "127.0.0.1:2180"
  }
}
```

#### Example Configuration File, with TLS

```javascript
{
  "datacenter": "east-aws",
  "data_dir": "/opt/consul",
  "log_level": "INFO",
  "node_name": "foobar",
  "server": true,
  "addresses": {
    "https": "0.0.0.0"
  },
  "ports": {
    "https": 8501
  },
  "key_file": "/etc/pki/tls/private/my.key",
  "cert_file": "/etc/pki/tls/certs/my.crt",
  "ca_file": "/etc/pki/tls/certs/ca-bundle.crt"
}
```

See, especially, the use of the `ports` setting:

```javascript
"ports": {
  "https": 8501
}
```

Consul will not enable TLS for the HTTP API unless the `https` port has been
assigned a port number `> 0`. We recommend using `8501` for `https` as this
default will automatically work with some tooling.

#### Configuration Key Reference

-> **Note:** All the TTL values described below are parsed by Go's `time` package, and have the following
[formatting specification](https://golang.org/pkg/time/#ParseDuration): "A
duration string is a possibly signed sequence of decimal numbers, each with
optional fraction and a unit suffix, such as '300ms', '-1.5h' or '2h45m'.
Valid time units are 'ns', 'us' (or 'µs'), 'ms', 's', 'm', 'h'."

- `acl` ((#acl)) - This object allows a number of sub-keys to be set which
  controls the ACL system. Configuring the ACL system within the ACL stanza was added
  in Consul 1.4.0

  The following sub-keys are available:

  - `enabled` ((#acl_enabled)) - Enables ACLs.

  - `policy_ttl` ((#acl_policy_ttl)) - Used to control Time-To-Live caching
    of ACL policies. By default, this is 30 seconds. This setting has a major performance
    impact: reducing it will cause more frequent refreshes while increasing it reduces
    the number of refreshes. However, because the caches are not actively invalidated,
    ACL policy may be stale up to the TTL value.

  - `role_ttl` ((#acl_role_ttl)) - Used to control Time-To-Live caching
    of ACL roles. By default, this is 30 seconds. This setting has a major performance
    impact: reducing it will cause more frequent refreshes while increasing it reduces
    the number of refreshes. However, because the caches are not actively invalidated,
    ACL role may be stale up to the TTL value.

  - `token_ttl` ((#acl_token_ttl)) - Used to control Time-To-Live caching
    of ACL tokens. By default, this is 30 seconds. This setting has a major performance
    impact: reducing it will cause more frequent refreshes while increasing it reduces
    the number of refreshes. However, because the caches are not actively invalidated,
    ACL token may be stale up to the TTL value.

  - `down_policy` ((#acl_down_policy)) - Either "allow", "deny", "extend-cache"
    or "async-cache"; "extend-cache" is the default. In the case that a policy or
    token cannot be read from the [`primary_datacenter`](#primary_datacenter) or
    leader node, the down policy is applied. In "allow" mode, all actions are permitted,
    "deny" restricts all operations, and "extend-cache" allows any cached objects
    to be used, ignoring their TTL values. If a non-cached ACL is used, "extend-cache"
    acts like "deny". The value "async-cache" acts the same way as "extend-cache"
    but performs updates asynchronously when ACL is present but its TTL is expired,
    thus, if latency is bad between the primary and secondary datacenters, latency
    of operations is not impacted.

  - `default_policy` ((#acl_default_policy)) - Either "allow" or "deny";
    defaults to "allow" but this will be changed in a future major release. The default
    policy controls the behavior of a token when there is no matching rule. In "allow"
    mode, ACLs are a denylist: any operation not specifically prohibited is allowed.
    In "deny" mode, ACLs are an allowlist: any operation not specifically
    allowed is blocked. **Note**: this will not take effect until you've enabled ACLs.

  - `enable_key_list_policy` ((#acl_enable_key_list_policy)) - Either "enabled"
    or "disabled", defaults to "disabled". When enabled, the `list` permission will
    be required on the prefix being recursively read from the KV store. Regardless
    of being enabled, the full set of KV entries under the prefix will be filtered
    to remove any entries that the request's ACL token does not grant at least read
    permissions. This option is only available in Consul 1.0 and newer.

  - `enable_token_replication` ((#acl_enable_token_replication)) - By default
    secondary Consul datacenters will perform replication of only ACL policies and
    roles. Setting this configuration will will enable ACL token replication and
    allow for the creation of both [local tokens](/api/acl/tokens#local) and
    [auth methods](/docs/acl/auth-methods) in connected secondary datacenters.

    ~> **Warning:** When enabling ACL token replication on the secondary datacenter,
    global tokens already present in the secondary datacenter will be lost. For
    production environments, consider configuring ACL replication in your initial
    datacenter bootstrapping process.

  - `enable_token_persistence` ((#acl_enable_token_persistence)) - Either
    `true` or `false`. When `true` tokens set using the API will be persisted to
    disk and reloaded when an agent restarts.

  - `tokens` ((#acl_tokens)) - This object holds all of the configured
    ACL tokens for the agents usage.

    - `master` ((#acl_tokens_master)) - Only used for servers in the [`primary_datacenter`](#primary_datacenter).
      This token will be created with management-level permissions if it does not
      exist. It allows operators to bootstrap the ACL system with a token Secret
      ID that is well-known.

      The `master` token is only installed when a server acquires cluster
      leadership. If you would like to install or change the `acl_master_token`,
      set the new value for `master` in the configuration for all servers. Once
      this is done, restart the current leader to force a leader election. If
      the `master` token is not supplied, then the servers do not create a
      master token. When you provide a value, it should be a UUID. To maintain
      backwards compatibility and an upgrade path this restriction is not
      currently enforced but will be in a future major Consul release.

    - `default` ((#acl_tokens_default)) - When provided, the agent will
      use this token when making requests to the Consul servers. Clients can override
      this token on a per-request basis by providing the "?token" query parameter.
      When not provided, the empty token, which maps to the 'anonymous' ACL token,
      is used.

    - `agent` ((#acl_tokens_agent)) - Used for clients and servers to perform
      internal operations. If this isn't specified, then the
      [`default`](#acl_tokens_default) will be used.

      This token must at least have write access to the node name it will
      register as in order to set any of the node-level information in the
      catalog such as metadata, or the node's tagged addresses.

    - `agent_master` ((#acl_tokens_agent_master)) - Used to access [agent endpoints](/api/agent)
      that require agent read or write privileges, or node read privileges, even if Consul servers aren't present to validate any tokens. This should only be used by operators during outages, regular ACL tokens should normally be used by applications.

    - `replication` ((#acl_tokens_replication)) - The ACL token used to
      authorize secondary datacenters with the primary datacenter for replication
      operations. This token is required for servers outside the [`primary_datacenter`](#primary_datacenter) when ACLs are enabled. This token may be provided later using the [agent token API](/api/agent#update-acl-tokens) on each server. This token must have at least "read" permissions on ACL data but if ACL token replication is enabled then it must have "write" permissions. This also enables Connect replication, for which the token will require both operator "write" and intention "read" permissions for replicating CA and Intention data.

      ~> **Warning:** When enabling ACL token replication on the secondary datacenter,
      policies and roles already present in the secondary datacenter will be lost. For
      production environments, consider configuring ACL replication in your initial
      datacenter bootstrapping process.

    - `managed_service_provider` ((#acl_tokens_managed_service_provider)) <EnterpriseAlert inline /> - An
      array of ACL tokens used by Consul managed service providers for cluster operations.

      ```json
      "managed_service_provider": [
        {
          "accessor_id": "ed22003b-0832-4e48-ac65-31de64e5c2ff",
          "secret_id": "cb6be010-bba8-4f30-a9ed-d347128dde17"
        }
      ]
      ```

- `acl_datacenter` - **This field is deprecated in Consul 1.4.0. See the [`primary_datacenter`](#primary_datacenter) field instead.**

  This designates the datacenter which is authoritative for ACL information. It must be provided to enable ACLs. All servers and datacenters must agree on the ACL datacenter. Setting it on the servers is all you need for cluster-level enforcement, but for the APIs to forward properly from the clients,
  it must be set on them too. In Consul 0.8 and later, this also enables agent-level enforcement
  of ACLs. Please review the [ACL tutorial](https://learn.hashicorp.com/tutorials/consul/access-control-setup-production) for more details.

- `acl_default_policy` ((#acl_default_policy_legacy)) - **Deprecated in Consul 1.4.0. See the [`acl.default_policy`](#acl_default_policy) field instead.**
  Either "allow" or "deny"; defaults to "allow". The default policy controls the
  behavior of a token when there is no matching rule. In "allow" mode, ACLs are a
  denylist: any operation not specifically prohibited is allowed. In "deny" mode,
  ACLs are an allowlist: any operation not specifically allowed is blocked. **Note**:
  this will not take effect until you've set `primary_datacenter` to enable ACL support.

- `acl_down_policy` ((#acl_down_policy_legacy)) - **Deprecated in Consul
  1.4.0. See the [`acl.down_policy`](#acl_down_policy) field instead.** Either "allow",
  "deny", "extend-cache" or "async-cache"; "extend-cache" is the default. In the
  case that the policy for a token cannot be read from the [`primary_datacenter`](#primary_datacenter)
  or leader node, the down policy is applied. In "allow" mode, all actions are permitted,
  "deny" restricts all operations, and "extend-cache" allows any cached ACLs to be
  used, ignoring their TTL values. If a non-cached ACL is used, "extend-cache" acts
  like "deny". The value "async-cache" acts the same way as "extend-cache" but performs
  updates asynchronously when ACL is present but its TTL is expired, thus, if latency
  is bad between ACL authoritative and other datacenters, latency of operations is
  not impacted.

- `acl_agent_master_token` ((#acl_agent_master_token_legacy)) - **Deprecated
  in Consul 1.4.0. See the [`acl.tokens.agent_master`](#acl_tokens_agent_master)
  field instead.** Used to access [agent endpoints](/api/agent) that
  require agent read or write privileges, or node read privileges, even if Consul
  servers aren't present to validate any tokens. This should only be used by operators
  during outages, regular ACL tokens should normally be used by applications. This
  was added in Consul 0.7.2 and is only used when [`acl_enforce_version_8`](#acl_enforce_version_8) is set to true.

- `acl_agent_token` ((#acl_agent_token_legacy)) - **Deprecated in Consul
  1.4.0. See the [`acl.tokens.agent`](#acl_tokens_agent) field instead.** Used for
  clients and servers to perform internal operations. If this isn't specified, then
  the [`acl_token`](#acl_token) will be used. This was added in Consul 0.7.2.

  This token must at least have write access to the node name it will register as in order to set any
  of the node-level information in the catalog such as metadata, or the node's tagged addresses.

- `acl_enforce_version_8` - **Deprecated in
  Consul 1.4.0 and removed in 1.8.0.** Used for clients and servers to determine if enforcement should
  occur for new ACL policies being previewed before Consul 0.8. Added in Consul 0.7.2,
  this defaults to false in versions of Consul prior to 0.8, and defaults to true
  in Consul 0.8 and later. This helps ease the transition to the new ACL features
  by allowing policies to be in place before enforcement begins.

- `acl_master_token` ((#acl_master_token_legacy)) - **Deprecated in Consul
  1.4.0. See the [`acl.tokens.master`](#acl_tokens_master) field instead.** Only
  used for servers in the [`primary_datacenter`](#primary_datacenter). This token
  will be created with management-level permissions if it does not exist. It allows
  operators to bootstrap the ACL system with a token ID that is well-known.

  The `acl_master_token` is only installed when a server acquires cluster leadership. If
  you would like to install or change the `acl_master_token`, set the new value for `acl_master_token`
  in the configuration for all servers. Once this is done, restart the current leader to force a
  leader election. If the `acl_master_token` is not supplied, then the servers do not create a master
  token. When you provide a value, it can be any string value. Using a UUID would ensure that it looks
  the same as the other tokens, but isn't strictly necessary.

- `acl_replication_token` ((#acl_replication_token_legacy)) - **Deprecated
  in Consul 1.4.0. See the [`acl.tokens.replication`](#acl_tokens_replication) field
  instead.** Only used for servers outside the [`primary_datacenter`](#primary_datacenter)
  running Consul 0.7 or later. When provided, this will enable [ACL replication](https://learn.hashicorp.com/tutorials/consul/access-control-replication-multiple-datacenters)
  using this ACL replication using this token to retrieve and replicate the ACLs
  to the non-authoritative local datacenter. In Consul 0.9.1 and later you can enable
  ACL replication using [`enable_acl_replication`](#enable_acl_replication) and then
  set the token later using the [agent token API](/api/agent#update-acl-tokens)
  on each server. If the `acl_replication_token` is set in the config, it will automatically
  set [`enable_acl_replication`](#enable_acl_replication) to true for backward compatibility.

  If there's a partition or other outage affecting the authoritative datacenter, and the
  [`acl_down_policy`](/docs/agent/options#acl_down_policy) is set to "extend-cache", tokens not
  in the cache can be resolved during the outage using the replicated set of ACLs.

- `acl_token` ((#acl_token_legacy)) - **Deprecated in Consul 1.4.0. See
  the [`acl.tokens.default`](#acl_tokens_default) field instead.** When provided,
  the agent will use this token when making requests to the Consul servers. Clients
  can override this token on a per-request basis by providing the "?token" query
  parameter. When not provided, the empty token, which maps to the 'anonymous' ACL
  policy, is used.

- `acl_ttl` ((#acl_ttl_legacy)) - **Deprecated in Consul 1.4.0. See the
  [`acl.token_ttl`](#acl_token_ttl) field instead.**Used to control Time-To-Live
  caching of ACLs. By default, this is 30 seconds. This setting has a major performance
  impact: reducing it will cause more frequent refreshes while increasing it reduces
  the number of refreshes. However, because the caches are not actively invalidated,
  ACL policy may be stale up to the TTL value.

- `addresses` - This is a nested object that allows setting
  bind addresses. In Consul 1.0 and later these can be set to a space-separated list
  of addresses to bind to, or a [go-sockaddr](https://godoc.org/github.com/hashicorp/go-sockaddr/template) template that can potentially resolve to multiple addresses.

  `http`, `https` and `grpc` all support binding to a Unix domain socket. A
  socket can be specified in the form `unix:///path/to/socket`. A new domain
  socket will be created at the given path. If the specified file path already
  exists, Consul will attempt to clear the file and create the domain socket
  in its place. The permissions of the socket file are tunable via the
  [`unix_sockets` config construct](#unix_sockets).

  When running Consul agent commands against Unix socket interfaces, use the
  `-http-addr` argument to specify the path to the socket. You can also place
  the desired values in the `CONSUL_HTTP_ADDR` environment variable.

  For TCP addresses, the environment variable value should be an IP address
  _with the port_. For example: `10.0.0.1:8500` and not `10.0.0.1`. However,
  ports are set separately in the [`ports`](#ports) structure when
  defining them in a configuration file.

  The following keys are valid:

  - `dns` - The DNS server. Defaults to `client_addr`
  - `http` - The HTTP API. Defaults to `client_addr`
  - `https` - The HTTPS API. Defaults to `client_addr`
  - `grpc` - The gRPC API. Defaults to `client_addr`

- `advertise_addr` Equivalent to the [`-advertise` command-line flag](#_advertise).

- `advertise_addr_ipv4` This was added together with [`advertise_addr_ipv6`](#advertise_addr_ipv6) to support dual stack IPv4/IPv6 environments. Using this, both IPv4 and IPv6 addresses can be specified and requested during eg service discovery.

- `advertise_addr_ipv6` This was added together with [`advertise_addr_ipv4`](#advertise_addr_ipv4) to support dual stack IPv4/IPv6 environments. Using this, both IPv4 and IPv6 addresses can be specified and requested during eg service discovery.

- `advertise_addr_wan` Equivalent to the [`-advertise-wan` command-line flag](#_advertise-wan).

- `advertise_addr_wan_ipv4` This was added together with [`advertise_addr_wan_ipv6`](#advertise_addr_wan_ipv6) to support dual stack IPv4/IPv6 environments. Using this, both IPv4 and IPv6 addresses can be specified and requested during eg service discovery.

- `advertise_addr_wan_ipv6` This was added together with [`advertise_addr_wan_ipv4`](#advertise_addr_wan_ipv4) to support dual stack IPv4/IPv6 environments. Using this, both IPv4 and IPv6 addresses can be specified and requested during eg service discovery.

- `serf_lan` ((#serf_lan_bind)) Equivalent to the [`-serf-lan-bind` command-line flag](#_serf_lan_bind).

- `serf_lan_allowed_cidrs` ((#serf_lan_allowed_cidrs)) Equivalent to the [`-serf-lan-allowed-cidrs` command-line flag](#_serf_lan_allowed_cidrs).

- `serf_wan` ((#serf_wan_bind)) Equivalent to the [`-serf-wan-bind` command-line flag](#_serf_wan_bind).

- `serf_wan_allowed_cidrs` ((#serf_wan_allowed_cidrs)) Equivalent to the [`-serf-wan-allowed-cidrs` command-line flag](#_serf_wan_allowed_cidrs).

- `audit` <EnterpriseAlert inline /> - Added in Consul 1.8, the audit object allow users to enable auditing
  and configure a sink and filters for their audit logs.

  ```hcl
    audit {
      enabled = true
      sink "My sink" {
        type   = "file"
        format = "json"
        path   = "data/audit/audit.json"
        delivery_guarantee = "best-effort"
        rotate_duration = "24h"
        rotate_max_files = 15
        rotate_bytes = 25165824
      }
  }
  ```

  The following sub-keys are available:

  - `enabled` - Controls whether Consul logs out each time a user
    performs an operation. ACLs must be enabled to use this feature. Defaults to `false`.

  - `sink` - This object provides configuration for the destination to which
    Consul will log auditing events. Sink is an object containing keys to sink objects, where the key is the name of the sink.

    - `type` - Type specifies what kind of sink this is.
      The following keys are valid:
      - `file` - Currently only file sinks are available, they take the following keys.
    - `format` - Format specifies what format the events will
      be emitted with.
      The following keys are valid:
      - `json` - Currently only json events are offered.
    - `path` - The directory and filename to write audit events to.
    - `delivery_guarantee` - Specifies
      the rules governing how audit events are written.
      The following keys are valid:
      - `best-effort` - Consul only supports `best-effort` event delivery.
    - `rotate_duration` - Specifies the
      interval by which the system rotates to a new log file. At least one of `rotate_duration` or `rotate_bytes`
      must be configured to enable audit logging.
    - `rotate_max_files` - Defines the
      limit that Consul should follow before it deletes old log files.
    - `rotate_bytes` - Specifies how large an
      individual log file can grow before Consul rotates to a new file. At least one of `rotate_bytes` or
      `rotate_duration` must be configured to enable audit logging.

- `autopilot` Added in Consul 0.8, this object allows a
  number of sub-keys to be set which can configure operator-friendly settings for
  Consul servers. When these keys are provided as configuration, they will only be
  respected on bootstrapping. If they are not provided, the defaults will be used.
  In order to change the value of these options after bootstrapping, you will need
  to use the [Consul Operator Autopilot](/docs/commands/operator/autopilot)
  command. For more information about Autopilot, review the [Autopilot tutorial](https://learn.hashicorp.com/tutorials/consul/autopilot-datacenter-operations).

  The following sub-keys are available:

  - `cleanup_dead_servers` - This controls the
    automatic removal of dead server nodes periodically and whenever a new server
    is added to the cluster. Defaults to `true`.

  - `last_contact_threshold` - Controls the
    maximum amount of time a server can go without contact from the leader before
    being considered unhealthy. Must be a duration value such as `10s`. Defaults
    to `200ms`.

  - `max_trailing_logs` - Controls the maximum number
    of log entries that a server can trail the leader by before being considered
    unhealthy. Defaults to 250.

  - `min_quorum` - Sets the minimum number of servers necessary
    in a cluster before autopilot can prune dead servers. There is no default.

  - `server_stabilization_time` - Controls
    the minimum amount of time a server must be stable in the 'healthy' state before
    being added to the cluster. Only takes effect if all servers are running Raft
    protocol version 3 or higher. Must be a duration value such as `30s`. Defaults
    to `10s`.

  - `redundancy_zone_tag` <EnterpriseAlert inline /> -
    This controls the [`-node-meta`](#_node_meta) key to use when Autopilot is separating
    servers into zones for redundancy. Only one server in each zone can be a voting
    member at one time. If left blank (the default), this feature will be disabled.

  - `disable_upgrade_migration` <EnterpriseAlert inline /> -
    If set to `true`, this setting will disable Autopilot's upgrade migration strategy
    in Consul Enterprise of waiting until enough newer-versioned servers have been
    added to the cluster before promoting any of them to voters. Defaults to `false`.

  - `upgrade_version_tag` <EnterpriseAlert inline /> -
    The node_meta tag to use for version info when performing upgrade migrations.
    If this is not set, the Consul version will be used.

- `auto_config` This object allows setting options for the `auto_config` feature.

  The following sub-keys are available:

  - `enabled` (Defaults to `false`) This option enables `auto_config` on a client
    agent. When starting up but before joining the cluster, the client agent will
    make an RPC to the configured server addresses to request configuration settings,
    such as its `agent` ACL token, TLS certificates, Gossip encryption key as well
    as other configuration settings. These configurations get merged in as defaults
    with any user-supplied configuration on the client agent able to override them.
    The initial RPC uses a JWT specified with either `intro_token`,
    `intro_token_file` or the `CONSUL_INTRO_TOKEN` environment variable to authorize
    the request. How the JWT token is verified is controlled by the `auto_config.authorizer`
    object available for use on Consul servers. Enabling this option also turns
    on Connect because it is vital for `auto_config`, more specifically the CA
    and certificates infrastructure.

  - `intro_token` (Defaults to `""`) This specifies the JWT to use for the initial
    `auto_config` RPC to the Consul servers. This can be overridden with the
    `CONSUL_INTRO_TOKEN` environment variable

  - `intro_token_file` (Defaults to `""`) This specifies a file containing the JWT
    to use for the initial `auto_config` RPC to the Consul servers. This token
    from this file is only loaded if the `intro_token` configuration is unset as
    well as the `CONSUL_INTRO_TOKEN` environment variable

  - `server_addresses` (Defaults to `[]`) This specifies the addresses of servers in
    the local datacenter to use for the initial RPC. These addresses support
    [Cloud Auto-Joining](#cloud-auto-joining) and can optionally include a port to
    use when making the outbound connection. If not port is provided the `server_port`
    will be used.

  - `dns_sans` (Defaults to `[]`) This is a list of extra DNS SANs to request in the
    client agent's TLS certificate. The `localhost` DNS SAN is always requested.

  - `ip_sans` (Defaults to `[]`) This is a list of extra IP SANs to request in the
    client agent's TLS certficate. The `::1` and `127.0.0.1` IP SANs are always requested.

  - `authorization` This object controls how a Consul server will authorize `auto_config`
    requests and in particular how to verify the JWT intro token.

    - `enabled` (Defaults to `false`) This option enables `auto_config` authorization
      capabilities on the server.

    - `static` This object controls configuring the static authorizer setup in the Consul
      configuration file. Almost all sub-keys are identical to those provided by the [JWT
      Auth Method](/docs/acl/auth-methods/jwt).

      - `jwt_validation_pub_keys` (Defaults to `[]`) A list of PEM-encoded public keys
        to use to authenticate signatures locally.

        Exactly one of `jwks_url` `jwt_validation_pub_keys`, or `oidc_discovery_url` is required.

      - `oidc_discovery_url` (Defaults to `""`) The OIDC Discovery URL, without any
        .well-known component (base path).

        Exactly one of `jwks_url` `jwt_validation_pub_keys`, or `oidc_discovery_url` is required.

      - `oidc_discovery_ca_cert` (Defaults to `""`) PEM encoded CA cert for use by the TLS
        client used to talk with the OIDC Discovery URL. NOTE: Every line must end
        with a newline (`\n`). If not set, system certificates are used.

      - `jwks_url` (Defaults to `""`) The JWKS URL to use to authenticate signatures.

        Exactly one of `jwks_url` `jwt_validation_pub_keys`, or `oidc_discovery_url` is required.

      - `jwks_ca_cert` (Defaults to `""`) PEM encoded CA cert for use by the TLS client
        used to talk with the JWKS URL. NOTE: Every line must end with a newline
        (`\n`). If not set, system certificates are used.

      - `claim_mappings` (Defaults to `(map[string]string)` Mappings of claims (key) that
        will be copied to a metadata field (value). Use this if the claim you are capturing
        is singular (such as an attribute).

        When mapped, the values can be any of a number, string, or boolean and will
        all be stringified when returned.

      - `list_claim_mappings` (Defaults to `(map[string]string)`) Mappings of claims (key)
        will be copied to a metadata field (value). Use this if the claim you are capturing
        is list-like (such as groups).

        When mapped, the values in each list can be any of a number, string, or
        boolean and will all be stringified when returned.

      - `jwt_supported_algs` (Defaults to `["RS256"]`) JWTSupportedAlgs is a list of
        supported signing algorithms.

      - `bound_audiences` (Defaults to `[]`) List of `aud` claims that are valid for
        login; any match is sufficient.

      - `bound_issuer` (Defaults to `""`) The value against which to match the `iss`
        claim in a JWT.

      - `expiration_leeway` (Defaults to `"0s"`) Duration of leeway when
        validating expiration of a token to account for clock skew. Defaults to 150s
        (2.5 minutes) if set to 0s and can be disabled if set to -1ns.

      - `not_before_leeway` (Defaults to `"0s"`) Duration of leeway when
        validating not before values of a token to account for clock skew. Defaults
        to 150s (2.5 minutes) if set to 0s and can be disabled if set to -1.

      - `clock_skew_leeway` (Defaults to `"0s"`) Duration of leeway when
        validating all claims to account for clock skew. Defaults to 60s (1 minute)
        if set to 0s and can be disabled if set to -1ns.

      - `claim_assertions` (Defaults to []) List of assertions about the mapped
        claims required to authorize the incoming RPC request. The syntax uses
        github.com/hashicorp/go-bexpr which is shared with the
        [API filtering feature](/api/features/filtering). For example, the following
        configurations when combined will ensure that the JWT `sub` matches the node
        name requested by the client.

        ```
        claim_mappings {
          sub = "node_name"
        }
        claim_assertions = [
          "value.node_name == \"${node}\""
        ]
        ```

        The assertions are lightly templated using [HIL syntax](https://github.com/hashicorp/hil)
        to interpolate some values from the RPC request. The list of variables that can be interpolated
        are:

        - `node` - The node name the client agent is requesting.

        - `segment` <EnterpriseAlert inline /> - The network segment name the client is requesting.

- `auto_encrypt` This object allows setting options for the `auto_encrypt` feature.

  The following sub-keys are available:

  - `allow_tls` (Defaults to `false`) This option enables
    `auto_encrypt` on the servers and allows them to automatically distribute certificates
    from the Connect CA to the clients. If enabled, the server can accept incoming
    connections from both the built-in CA and the Connect CA, as well as their certificates.
    Note, the server will only present the built-in CA and certificate, which the
    client can verify using the CA it received from `auto_encrypt` endpoint. If disabled,
    a client configured with `auto_encrypt.tls` will be unable to start.

  - `tls` (Defaults to `false`) Allows the client to request the
    Connect CA and certificates from the servers, for encrypting RPC communication.
    The client will make the request to any servers listed in the `-join` or `-retry-join`
    option. This requires that every server to have `auto_encrypt.allow_tls` enabled.
    When both `auto_encrypt` options are used, it allows clients to receive certificates
    that are generated on the servers. If the `-server-port` is not the default one,
    it has to be provided to the client as well. Usually this is discovered through
    LAN gossip, but `auto_encrypt` provision happens before the information can be
    distributed through gossip. The most secure `auto_encrypt` setup is when the
    client is provided with the built-in CA, `verify_server_hostname` is turned on,
    and when an ACL token with `node.write` permissions is setup. It is also possible
    to use `auto_encrypt` with a CA and ACL, but without `verify_server_hostname`,
    or only with a ACL enabled, or only with CA and `verify_server_hostname`, or
    only with a CA, or finally without a CA and without ACL enabled. In any case,
    the communication to the `auto_encrypt` endpoint is always TLS encrypted.

  - `dns_san` (Defaults to `[]`) When this option is being
    used, the certificates requested by `auto_encrypt` from the server have these
    `dns_san` set as DNS SAN.

  - `ip_san` (Defaults to `[]`) When this option is being used,
    the certificates requested by `auto_encrypt` from the server have these `ip_san`
    set as IP SAN.

- `bootstrap` Equivalent to the [`-bootstrap` command-line flag](#_bootstrap).

- `bootstrap_expect` Equivalent to the [`-bootstrap-expect` command-line flag](#_bootstrap_expect).

- `bind_addr` Equivalent to the [`-bind` command-line flag](#_bind).

  This parameter can be set to a go-sockaddr template that resolves to a single
  address. Special characters such as blackslashes `\` or double quotes `"`
  within a double quoted string value must be escaped with a backslash `\`.
  Some example templates:

  <Tabs>
  <Tab heading="HCL">

  ```hcl
  bind_addr = "{{ GetPrivateInterfaces | include \"network\" \"10.0.0.0/8\" | attr \"address\" }}"
  ```
  </Tab>
  <Tab heading="JSON">

  ```json
  {
    "bind_addr": "{{ GetPrivateInterfaces | include \"network\" \"10.0.0.0/8\" | attr \"address\" }}"
  }
  ```
  </Tab>
  </Tabs>

- `cache` Cache configuration of agent. The configurable values are the following:

  - `entry_fetch_max_burst`: The size of the token bucket used to recharge the rate-limit per
    cache entry. The default value is 2 and means that when cache has not been updated
    for a long time, 2 successive queries can be made as long as the rate-limit is not
    reached.

  - `entry_fetch_rate`: configures the rate-limit at which the cache may refresh a single
    entry. On a cluster with many changes/s, watching changes in the cache might put high
    pressure on the servers. This ensures the number of requests for a single cache entry
    will never go beyond this limit, even when a given service changes every 1/100s.
    Since this is a per cache entry limit, having a highly unstable service will only rate
    limit the watched on this service, but not the other services/entries.
    The value is strictly positive, expressed in queries per second as a float,
    1 means 1 query per second, 0.1 mean 1 request every 10s maximum.
    The default value is "No limit" and should be tuned on large
    clusters to avoid performing too many RPCs on entries changing a lot.

- `ca_file` This provides a file path to a PEM-encoded certificate
  authority. The certificate authority is used to check the authenticity of client
  and server connections with the appropriate [`verify_incoming`](#verify_incoming)
  or [`verify_outgoing`](#verify_outgoing) flags.

- `ca_path` This provides a path to a directory of PEM-encoded
  certificate authority files. These certificate authorities are used to check the
  authenticity of client and server connections with the appropriate [`verify_incoming`](#verify_incoming) or [`verify_outgoing`](#verify_outgoing) flags.

- `cert_file` This provides a file path to a PEM-encoded
  certificate. The certificate is provided to clients or servers to verify the agent's
  authenticity. It must be provided along with [`key_file`](#key_file).

- `check_update_interval` ((#check_update_interval))
  This interval controls how often check output from checks in a steady state is
  synchronized with the server. By default, this is set to 5 minutes ("5m"). Many
  checks which are in a steady state produce slightly different output per run (timestamps,
  etc) which cause constant writes. This configuration allows deferring the sync
  of check output for a given interval to reduce write pressure. If a check ever
  changes state, the new state and associated output is synchronized immediately.
  To disable this behavior, set the value to "0s".

- `client_addr` Equivalent to the [`-client` command-line flag](#_client).

- `config_entries` This object allows setting options for centralized config entries.

  The following sub-keys are available:

  - `bootstrap` ((#config_entries_bootstrap))
    This is a list of inlined config entries to insert into the state store when
    the Consul server gains leadership. This option is only applicable to server
    nodes. Each bootstrap entry will be created only if it does not exist. When reloading,
    any new entries that have been added to the configuration will be processed.
    See the [configuration entry docs](/docs/agent/config_entries) for more
    details about the contents of each entry.

- `connect` This object allows setting options for the Connect feature.

  The following sub-keys are available:

  - `enabled` ((#connect_enabled)) Controls whether Connect features are
    enabled on this agent. Should be enabled on all clients and servers in the cluster
    in order for Connect to function properly. Defaults to false.

  - `enable_mesh_gateway_wan_federation` ((#connect_enable_mesh_gateway_wan_federation)) Controls whether cross-datacenter federation traffic between servers is funneled
    through mesh gateways. Defaults to false. This was added in Consul 1.8.0.

  - `ca_provider` ((#connect_ca_provider)) Controls which CA provider to
    use for Connect's CA. Currently only the `consul` and `vault` providers are supported.
    This is only used when initially bootstrapping the cluster. For an existing cluster,
    use the [Update CA Configuration Endpoint](/api/connect/ca#update-ca-configuration).

  - `ca_config` ((#connect_ca_config)) An object which allows setting different
    config options based on the CA provider chosen. This is only used when initially
    bootstrapping the cluster. For an existing cluster, use the [Update CA Configuration
    Endpoint](/api/connect/ca#update-ca-configuration).

    The following providers are supported:

    #### Consul CA Provider (`ca_provider = "consul"`)

    - `private_key` ((#consul_ca_private_key)) The PEM contents of the
      private key to use for the CA.

    - `root_cert` ((#consul_ca_root_cert)) The PEM contents of the root
      certificate to use for the CA.

    #### Vault CA Provider (`ca_provider = "vault"`)

    - `address` ((#vault_ca_address)) The address of the Vault server to
      connect to.

    - `token` ((#vault_ca_token)) The Vault token to use.

    - `root_pki_path` ((#vault_ca_root_pki)) The path to use for the root
      CA pki backend in Vault. This can be an existing backend with a CA already
      configured, or a blank/unmounted backend in which case Connect will automatically
      mount/generate the CA. The Vault token given above must have `sudo` access
      to this backend, as well as permission to mount the backend at this path if
      it is not already mounted.

    - `intermediate_pki_path` ((#vault_ca_intermediate_pki))
      The path to use for the temporary intermediate CA pki backend in Vault. **Connect
      will overwrite any data at this path in order to generate a temporary intermediate
      CA**. The Vault token given above must have `write` access to this backend,
      as well as permission to mount the backend at this path if it is not already
      mounted.

    #### Common CA Config Options

    There are also a number of common configuration options supported by all providers:

    - `csr_max_concurrent` ((#ca_csr_max_concurrent)) Sets a limit on how
      many Certificate Signing Requests will be processed concurrently. Defaults
      to 0 (disabled). This is useful when you have more than one or two cores available
      to the server. For example on an 8 core server, setting this to 1 will ensure
      that even during a CA rotation no more than one server core on the leader will
      be consumed at a time with generating new certificates. Setting this is recommended
      **instead** of `csr_max_per_second` where you know there are multiple cores available
      since it is simpler to reason about limiting CSR resources this way without
      artificially slowing down rotations. Added in 1.4.1.

    - `csr_max_per_second` ((#ca_csr_max_per_second)) Sets a rate limit
      on the maximum number of Certificate Signing Requests (CSRs) the servers will
      accept. This is used to prevent CA rotation from causing unbounded CPU usage
      on servers. It defaults to 50 which is conservative - a 2017 Macbook can process
      about 100 per second using only ~40% of one CPU core - but sufficient for deployments
      up to ~1500 service instances before the time it takes to rotate is impacted.
      For larger deployments we recommend increasing this based on the expected number
      of server instances and server resources, or use `csr_max_concurrent` instead
      if servers have more than one core. Setting this to zero disables rate limiting.
      Added in 1.4.1.

    - `leaf_cert_ttl` ((#ca_leaf_cert_ttl)) The upper bound on the lease
      duration of a leaf certificate issued for a service. In most cases a new leaf
      certificate will be requested by a proxy before this limit is reached. This
      is also the effective limit on how long a server outage can last (with no leader)
      before network connections will start being rejected, and as a result the defaults
      is `72h` to last through a weekend without intervention. This value cannot
      be lower than 1 hour or higher than 1 year.

      This value is also used when rotating out old root certificates from
      the cluster. When a root certificate has been inactive (rotated out)
      for more than twice the _current_ `leaf_cert_ttl`, it will be removed
      from the trusted list.

    - `private_key_type` ((#ca_private_key_type)) The type of key to generate
      for this CA. This is only used when the provider is generating a new key. If
      `private_key` is set for the Consul provider, or existing root or intermediate
      PKI paths given for Vault then this will be ignored. Currently supported options
      are `ec` or `rsa`. Default is `ec`.

      It is required that all servers in a Datacenter have
      the same config for the CA. It is recommended that servers in
      different Datacenters have the same CA config for key type and size
      although the built-in CA and Vault provider will both allow mixed CA
      key types.

      Some CA providers (currently Vault) will not allow cross-signing a
      new CA certificate with a different key type. This means that if you
      migrate from an RSA-keyed Vault CA to an EC-keyed CA from any
      provider, you may have to proceed without cross-signing which risks
      temporary connection issues for workloads during the new certificate
      rollout. We highly recommend testing this outside of production to
      understand the impact and suggest sticking to same key type where
      possible.

      Note that this only affects _CA_ keys generated by the provider.
      Leaf certificate keys are always EC 256 regardless of the CA
      configuration.

    - `private_key_bits` ((#ca_private_key_bits)) The length of key to
      generate for this CA. This is only used when the provider is generating a new
      key. If `private_key` is set for the Consul provider, or existing root or intermediate
      PKI paths given for Vault then this will be ignored.

      Currently supported values are:

      - `private_key_type = ec` (default): `224, 256, 384, 521`
        corresponding to the NIST P-\* curves of the same name.
      - `private_key_type = rsa`: `2048, 4096`

- `datacenter` Equivalent to the [`-datacenter` command-line flag](#_datacenter).

- `data_dir` Equivalent to the [`-data-dir` command-line flag](#_data_dir).

- `disable_anonymous_signature` Disables providing an anonymous
  signature for de-duplication with the update check. See [`disable_update_check`](#disable_update_check).

- `disable_host_node_id` Equivalent to the [`-disable-host-node-id` command-line flag](#_disable_host_node_id).

- `disable_http_unprintable_char_filter` Defaults to false. Consul 1.0.3 fixed a potential security vulnerability where malicious users could craft KV keys with unprintable chars that would confuse operators using the CLI or UI into taking wrong actions. Users who had data written in older versions of Consul that did not have this restriction will be unable to deletethose values by default in 1.0.3 or later. This setting enables those users to **temporarily** disable the filter such that delete operations can work on those keys again to get back to a healthy state. It is strongly recommended that this filter is not disabled permanently as it exposes the original security vulnerability.

- `disable_remote_exec` Disables support for remote execution. When set to true, the agent will ignore
  any incoming remote exec requests. In versions of Consul prior to 0.8, this defaulted
  to false. In Consul 0.8 the default was changed to true, to make remote exec opt-in
  instead of opt-out.

- `disable_update_check` Disables automatic checking for security bulletins and new version releases. This is disabled in Consul Enterprise.

- `discard_check_output` Discards the output of health checks before storing them. This reduces the number of writes to the Consul raft log in environments where health checks have volatile output like timestamps, process ids, ...

- `discovery_max_stale` - Enables stale requests for all service discovery HTTP endpoints. This is
  equivalent to the [`max_stale`](#max_stale) configuration for DNS requests. If this value is zero (default), all service discovery HTTP endpoints are forwarded to the leader. If this value is greater than zero, any Consul server can handle the service discovery request. If a Consul server is behind the leader by more than `discovery_max_stale`, the query will be re-evaluated on the leader to get more up-to-date results. Consul agents also add a new `X-Consul-Effective-Consistency` response header which indicates if the agent did a stale read. `discover-max-stale` was introduced in Consul 1.0.7 as a way for Consul operators to force stale requests from clients at the agent level, and defaults to zero which matches default consistency behavior in earlier Consul versions.

- `dns_config` This object allows a number of sub-keys
  to be set which can tune how DNS queries are serviced. Check the tutorial on [DNS caching](https://learn.hashicorp.com/tutorials/consul/dns-caching) for more detail.

  The following sub-keys are available:

  - `allow_stale` - Enables a stale query for DNS information.
    This allows any Consul server, rather than only the leader, to service the request.
    The advantage of this is you get linear read scalability with Consul servers.
    In versions of Consul prior to 0.7, this defaulted to false, meaning all requests
    are serviced by the leader, providing stronger consistency but less throughput
    and higher latency. In Consul 0.7 and later, this defaults to true for better
    utilization of available servers.

  - `max_stale` - When [`allow_stale`](#allow_stale) is
    specified, this is used to limit how stale results are allowed to be. If a Consul
    server is behind the leader by more than `max_stale`, the query will be re-evaluated
    on the leader to get more up-to-date results. Prior to Consul 0.7.1 this defaulted
    to 5 seconds; in Consul 0.7.1 and later this defaults to 10 years ("87600h")
    which effectively allows DNS queries to be answered by any server, no matter
    how stale. In practice, servers are usually only milliseconds behind the leader,
    so this lets Consul continue serving requests in long outage scenarios where
    no leader can be elected.

  - `node_ttl` - By default, this is "0s", so all node lookups
    are served with a 0 TTL value. DNS caching for node lookups can be enabled by
    setting this value. This should be specified with the "s" suffix for second or
    "m" for minute.

  - `service_ttl` - This is a sub-object which allows
    for setting a TTL on service lookups with a per-service policy. The "\*" wildcard
    service can be used when there is no specific policy available for a service.
    By default, all services are served with a 0 TTL value. DNS caching for service
    lookups can be enabled by setting this value.

  - `enable_truncate` - If set to true, a UDP DNS
    query that would return more than 3 records, or more than would fit into a valid
    UDP response, will set the truncated flag, indicating to clients that they should
    re-query using TCP to get the full set of records.

  - `only_passing` - If set to true, any nodes whose
    health checks are warning or critical will be excluded from DNS results. If false,
    the default, only nodes whose healthchecks are failing as critical will be excluded.
    For service lookups, the health checks of the node itself, as well as the service-specific
    checks are considered. For example, if a node has a health check that is critical
    then all services on that node will be excluded because they are also considered
    critical.

  - `recursor_timeout` - Timeout used by Consul when
    recursively querying an upstream DNS server. See [`recursors`](#recursors) for more details. Default is 2s. This is available in Consul 0.7 and later.

  - `disable_compression` - If set to true, DNS
    responses will not be compressed. Compression was added and enabled by default
    in Consul 0.7.

  - `udp_answer_limit` - Limit the number of resource
    records contained in the answer section of a UDP-based DNS response. This parameter
    applies only to UDP DNS queries that are less than 512 bytes. This setting is
    deprecated and replaced in Consul 1.0.7 by [`a_record_limit`](#a_record_limit).

  - `a_record_limit` - Limit the number of resource
    records contained in the answer section of a A, AAAA or ANY DNS response (both
    TCP and UDP). When answering a question, Consul will use the complete list of
    matching hosts, shuffle the list randomly, and then limit the number of answers
    to `a_record_limit` (default: no limit). This limit does not apply to SRV records.

    In environments where [RFC 3484 Section 6](https://tools.ietf.org/html/rfc3484#section-6) Rule 9
    is implemented and enforced (i.e. DNS answers are always sorted and
    therefore never random), clients may need to set this value to `1` to
    preserve the expected randomized distribution behavior (note:
    [RFC 3484](https://tools.ietf.org/html/rfc3484) has been obsoleted by
    [RFC 6724](https://tools.ietf.org/html/rfc6724) and as a result it should
    be increasingly uncommon to need to change this value with modern
    resolvers).

  - `enable_additional_node_meta_txt` - When set to true, Consul
    will add TXT records for Node metadata into the Additional section of the DNS responses for several query types such as SRV queries. When set to false those records are not emitted. This does not impact the behavior of those same TXT records when they would be added to the Answer section of the response like when querying with type TXT or ANY. This defaults to true.

  - `soa` Allow to tune the setting set up in SOA. Non specified
    values fallback to their default values, all values are integers and expressed
    as seconds.

    The following settings are available:

    - `expire` ((#soa_expire)) - Configure SOA Expire duration in seconds,
      default value is 86400, ie: 24 hours.

    - `min_ttl` ((#soa_min_ttl)) - Configure SOA DNS minimum TTL. As explained
      in [RFC-2308](https://tools.ietf.org/html/rfc2308) this also controls negative
      cache TTL in most implementations. Default value is 0, ie: no minimum delay
      or negative TTL.

    - `refresh` ((#soa_refresh)) - Configure SOA Refresh duration in seconds,
      default value is `3600`, ie: 1 hour.

    - `retry` ((#soa_retry)) - Configures the Retry duration expressed
      in seconds, default value is 600, ie: 10 minutes.

  - `use_cache` ((#dns_use_cache)) - When set to true, DNS resolution will
    use the agent cache described in [agent caching](/api/features/caching).
    This setting affects all service and prepared queries DNS requests. Implies [`allow_stale`](#allow_stale)

  - `cache_max_age` ((#dns_cache_max_age)) - When [use_cache](#dns_use_cache)
    is enabled, the agent will attempt to re-fetch the result from the servers if
    the cached value is older than this duration. See: [agent caching](/api/features/caching).

    **Note** that unlike the `max-age` HTTP header, a value of 0 for this field is
    equivalent to "no max age". To get a fresh value from the cache use a very small value
    of `1ns` instead of 0.

  - `prefer_namespace` ((#dns_prefer_namespace)) <EnterpriseAlert inline /> -
    When set to true, in a DNS query for a service, the label between the domain
    and the `service` label will be treated as a namespace name instead of a datacenter.
    When set to false, the default, the behavior will be the same as non-Enterprise
    versions and will assume the label is the datacenter. See: [this section](/docs/agent/dns#namespaced-services)
    for more details.

- `domain` Equivalent to the [`-domain` command-line flag](#_domain).

- `enable_acl_replication` When set on a Consul server, enables ACL replication without having to set
  the replication token via [`acl_replication_token`](#acl_replication_token). Instead, enable ACL replication
  and then introduce the token using the [agent token API](/api/agent#update-acl-tokens) on each server.
  See [`acl_replication_token`](#acl_replication_token) for more details.

  ~> **Warning:** When enabling ACL token replication on the secondary datacenter,
  policies and roles already present in the secondary datacenter will be lost. For
  production environments, consider configuring ACL replication in your initial
  datacenter bootstrapping process.

- `enable_agent_tls_for_checks` When set, uses a subset of the agent's TLS configuration (`key_file`,
  `cert_file`, `ca_file`, `ca_path`, and `server_name`) to set up the client for HTTP or gRPC health checks. This allows services requiring 2-way TLS to be checked using the agent's credentials. This was added in Consul 1.0.1 and defaults to false.

- `enable_central_service_config` When set, the Consul agent will look for any centralized service
  configurations that match a registering service instance. If it finds any, the agent will merge the centralized defaults with the service instance configuration. This allows for things like service protocol or proxy configuration to be defined centrally and inherited by any affected service registrations.

- `enable_debug` When set, enables some additional debugging features. Currently, this is only used to
  access runtime profiling HTTP endpoints, which are available with an `operator:read` ACL regardless of the value of `enable_debug`.

- `enable_script_checks` Equivalent to the [`-enable-script-checks` command-line flag](#_enable_script_checks).

  ~> **Security Warning:** Enabling script checks in some configurations may
  introduce a remote execution vulnerability which is known to be targeted by
  malware. We strongly recommend `enable_local_script_checks` instead. See [this
  blog post](https://www.hashicorp.com/blog/protecting-consul-from-rce-risk-in-specific-configurations)
  for more details.

- `enable_local_script_checks` Equivalent to the [`-enable-local-script-checks` command-line flag](#_enable_local_script_checks).

- `enable_syslog` Equivalent to the [`-syslog` command-line flag](#_syslog).

- `encrypt` Equivalent to the [`-encrypt` command-line flag](#_encrypt).

- `encrypt_verify_incoming` - This is an optional
  parameter that can be used to disable enforcing encryption for incoming gossip
  in order to upshift from unencrypted to encrypted gossip on a running cluster.
  See [this section](/docs/agent/encryption#configuring-gossip-encryption-on-an-existing-cluster)
  for more information. Defaults to true.

- `encrypt_verify_outgoing` - This is an optional
  parameter that can be used to disable enforcing encryption for outgoing gossip
  in order to upshift from unencrypted to encrypted gossip on a running cluster.
  See [this section](/docs/agent/encryption#configuring-gossip-encryption-on-an-existing-cluster)
  for more information. Defaults to true.

- `disable_keyring_file` - Equivalent to the
  [`-disable-keyring-file` command-line flag](#_disable_keyring_file).

- `gossip_lan` - **(Advanced)** This object contains a
  number of sub-keys which can be set to tune the LAN gossip communications. These
  are only provided for users running especially large clusters that need fine tuning
  and are prepared to spend significant effort correctly tuning them for their environment
  and workload. **Tuning these improperly can cause Consul to fail in unexpected
  ways**. The default values are appropriate in almost all deployments.

  - `gossip_nodes` - The number of random nodes to send
    gossip messages to per gossip_interval. Increasing this number causes the gossip
    messages to propagate across the cluster more quickly at the expense of increased
    bandwidth. The default is 3.

  - `gossip_interval` - The interval between sending
    messages that need to be gossiped that haven't been able to piggyback on probing
    messages. If this is set to zero, non-piggyback gossip is disabled. By lowering
    this value (more frequent) gossip messages are propagated across the cluster
    more quickly at the expense of increased bandwidth. The default is 200ms.

  - `probe_interval` - The interval between random
    node probes. Setting this lower (more frequent) will cause the cluster to detect
    failed nodes more quickly at the expense of increased bandwidth usage. The default
    is 1s.

  - `probe_timeout` - The timeout to wait for an ack
    from a probed node before assuming it is unhealthy. This should be at least the
    99-percentile of RTT (round-trip time) on your network. The default is 500ms
    and is a conservative value suitable for almost all realistic deployments.

  - `retransmit_mult` - The multiplier for the number
    of retransmissions that are attempted for messages broadcasted over gossip. The
    number of retransmits is scaled using this multiplier and the cluster size. The
    higher the multiplier, the more likely a failed broadcast is to converge at the
    expense of increased bandwidth. The default is 4.

  - `suspicion_mult` - The multiplier for determining
    the time an inaccessible node is considered suspect before declaring it dead.
    The timeout is scaled with the cluster size and the probe_interval. This allows
    the timeout to scale properly with expected propagation delay with a larger cluster
    size. The higher the multiplier, the longer an inaccessible node is considered
    part of the cluster before declaring it dead, giving that suspect node more time
    to refute if it is indeed still alive. The default is 4.

- `gossip_wan` - **(Advanced)** This object contains a
  number of sub-keys which can be set to tune the WAN gossip communications. These
  are only provided for users running especially large clusters that need fine tuning
  and are prepared to spend significant effort correctly tuning them for their environment
  and workload. **Tuning these improperly can cause Consul to fail in unexpected
  ways**. The default values are appropriate in almost all deployments.

  - `gossip_nodes` - The number of random nodes to send
    gossip messages to per gossip_interval. Increasing this number causes the gossip
    messages to propagate across the cluster more quickly at the expense of increased
    bandwidth. The default is 3.

  - `gossip_interval` - The interval between sending
    messages that need to be gossiped that haven't been able to piggyback on probing
    messages. If this is set to zero, non-piggyback gossip is disabled. By lowering
    this value (more frequent) gossip messages are propagated across the cluster
    more quickly at the expense of increased bandwidth. The default is 200ms.

  - `probe_interval` - The interval between random
    node probes. Setting this lower (more frequent) will cause the cluster to detect
    failed nodes more quickly at the expense of increased bandwidth usage. The default
    is 1s.

  - `probe_timeout` - The timeout to wait for an ack
    from a probed node before assuming it is unhealthy. This should be at least the
    99-percentile of RTT (round-trip time) on your network. The default is 500ms
    and is a conservative value suitable for almost all realistic deployments.

  - `retransmit_mult` - The multiplier for the number
    of retransmissions that are attempted for messages broadcasted over gossip. The
    number of retransmits is scaled using this multiplier and the cluster size. The
    higher the multiplier, the more likely a failed broadcast is to converge at the
    expense of increased bandwidth. The default is 4.

  - `suspicion_mult` - The multiplier for determining
    the time an inaccessible node is considered suspect before declaring it dead.
    The timeout is scaled with the cluster size and the probe_interval. This allows
    the timeout to scale properly with expected propagation delay with a larger cluster
    size. The higher the multiplier, the longer an inaccessible node is considered
    part of the cluster before declaring it dead, giving that suspect node more time
    to refute if it is indeed still alive. The default is 4.

- `key_file` This provides a the file path to a PEM-encoded
  private key. The key is used with the certificate to verify the agent's authenticity.
  This must be provided along with [`cert_file`](#cert_file).

- `http_config` This object allows setting options for the HTTP API and UI.

  The following sub-keys are available:

  - `block_endpoints`
    This object is a list of HTTP API endpoint prefixes to block on the agent, and
    defaults to an empty list, meaning all endpoints are enabled. Any endpoint that
    has a common prefix with one of the entries on this list will be blocked and
    will return a 403 response code when accessed. For example, to block all of the
    V1 ACL endpoints, set this to `["/v1/acl"]`, which will block `/v1/acl/create`,
    `/v1/acl/update`, and the other ACL endpoints that begin with `/v1/acl`. This
    only works with API endpoints, not `/ui` or `/debug`, those must be disabled
    with their respective configuration options. Any CLI commands that use disabled
    endpoints will no longer function as well. For more general access control, Consul's
    [ACL system](https://learn.hashicorp.com/tutorials/consul/access-control-setup-production)
    should be used, but this option is useful for removing access to HTTP API endpoints
    completely, or on specific agents. This is available in Consul 0.9.0 and later.

  - `response_headers` This object allows adding headers to the HTTP API and UI responses. For example, the following config can be used to enable [CORS](https://en.wikipedia.org/wiki/Cross-origin_resource_sharing) on the HTTP API endpoints:

    ```json
    {
      "http_config": {
        "response_headers": {
          "Access-Control-Allow-Origin": "*"
        }
      }
    }
    ```

  - `allow_write_http_from` This object is a list of networks in CIDR notation (eg "127.0.0.0/8") that are allowed to call the agent write endpoints. It defaults to an empty list, which means all networks are allowed. This is used to make the agent read-only, except for select ip ranges. - To block write calls from anywhere, use `[ "255.255.255.255/32" ]`. - To only allow write calls from localhost, use `[ "127.0.0.0/8" ]` - To only allow specific IPs, use `[ "10.0.0.1/32", "10.0.0.2/32" ]`

  - `use_cache` Defaults to true. If disabled, the agent won't be using [agent caching](/api/features/caching) to answer the request. Even when the url parameter is provided.

- `leave_on_terminate` If enabled, when the agent receives a TERM signal, it will send a `Leave` message to the rest of the cluster and gracefully leave. The default behavior for this feature varies based on whether or not the agent is running as a client or a server (prior to Consul 0.7 the default value was unconditionally set to `false`). On agents in client-mode, this defaults to `true` and for agents in server-mode, this defaults to `false`.

- `limits` Available in Consul 0.9.3 and later, this is a nested
  object that configures limits that are enforced by the agent. Prior to Consul 1.5.2,
  this only applied to agents in client mode, not Consul servers. The following parameters
  are available:

  - `http_max_conns_per_client` - Configures a limit of how many concurrent TCP connections a single client IP address is allowed to open to the agent's HTTP(S) server. This affects the HTTP(S) servers in both client and server agents. Default value is `200`.
  - `https_handshake_timeout` - Configures the limit for how long the HTTPS server in both client and server agents will wait for a client to complete a TLS handshake. This should be kept conservative as it limits how many connections an unauthenticated attacker can open if `verify_incoming` is being using to authenticate clients (strongly recommended in production). Default value is `5s`.
  - `rpc_handshake_timeout` - Configures the limit for how long servers will wait after a client TCP connection is established before they complete the connection handshake. When TLS is used, the same timeout applies to the TLS handshake separately from the initial protocol negotiation. All Consul clients should perform this immediately on establishing a new connection. This should be kept conservative as it limits how many connections an unauthenticated attacker can open if `verify_incoming` is being using to authenticate clients (strongly recommended in production). When `verify_incoming` is true on servers, this limits how long the connection socket and associated goroutines will be held open before the client successfully authenticates. Default value is `5s`.
  - `rpc_max_conns_per_client` - Configures a limit of how many concurrent TCP connections a single source IP address is allowed to open to a single server. It affects both clients connections and other server connections. In general Consul clients multiplex many RPC calls over a single TCP connection so this can typically be kept low. It needs to be more than one though since servers open at least one additional connection for raft RPC, possibly more for WAN federation when using network areas, and snapshot requests from clients run over a separate TCP conn. A reasonably low limit significantly reduces the ability of an unauthenticated attacker to consume unbounded resources by holding open many connections. You may need to increase this if WAN federated servers connect via proxies or NAT gateways or similar causing many legitimate connections from a single source IP. Default value is `100` which is designed to be extremely conservative to limit issues with certain deployment patterns. Most deployments can probably reduce this safely. 100 connections on modern server hardware should not cause a significant impact on resource usage from an unauthenticated attacker though.
  - `rpc_rate` - Configures the RPC rate limiter on Consul _clients_ by setting the maximum request rate that this agent is allowed to make for RPC requests to Consul servers, in requests per second. Defaults to infinite, which disables rate limiting.
  - `rpc_max_burst` - The size of the token bucket used to recharge the RPC rate limiter on Consul _clients_. Defaults to 1000 tokens, and each token is good for a single RPC call to a Consul server. See https://en.wikipedia.org/wiki/Token_bucket for more details about how token bucket rate limiters operate.
  - `kv_max_value_size` - **(Advanced)** Configures the maximum number of bytes for a kv request body to the [`/v1/kv`](/api/kv) endpoint. This limit defaults to [raft's](https://github.com/hashicorp/raft) suggested max size (512KB). **Note that tuning these improperly can cause Consul to fail in unexpected ways**, it may potentially affect leadership stability and prevent timely heartbeat signals by increasing RPC IO duration. This option affects the txn endpoint too, but Consul 1.7.2 introduced `txn_max_req_len` which is the preferred way to set the limit for the txn endpoint. If both limits are set, the higher one takes precedence.
  - `txn_max_req_len` - **(Advanced)** Configures the maximum number of bytes for a transaction request body to the [`/v1/txn`](/api/txn) endpoint. This limit defaults to [raft's](https://github.com/hashicorp/raft) suggested max size (512KB). **Note that tuning these improperly can cause Consul to fail in unexpected ways**, it may potentially affect leadership stability and prevent timely heartbeat signals by increasing RPC IO duration.

- `log_file` Equivalent to the [`-log-file` command-line flag](#_log_file).

- `log_rotate_duration` Equivalent to the [`-log-rotate-duration` command-line flag](#_log_rotate_duration).

- `log_rotate_bytes` Equivalent to the [`-log-rotate-bytes` command-line flag](#_log_rotate_bytes).

- `log_rotate_max_files` Equivalent to the [`-log-rotate-max-files` command-line flag](#_log_rotate_max_files).

- `log_level` Equivalent to the [`-log-level` command-line flag](#_log_level).

- `log_json` Equivalent to the [`-log-json` command-line flag](#_log_json).

- `default_query_time` Equivalent to the [`-default-query-time` command-line flag](#_default_query_time).

- `max_query_time` Equivalent to the [`-max-query-time` command-line flag](#_max_query_time).

- `node_id` Equivalent to the [`-node-id` command-line flag](#_node_id).

- `node_name` Equivalent to the [`-node` command-line flag](#_node).

- `node_meta` Available in Consul 0.7.3 and later, This object allows associating arbitrary metadata key/value pairs with the local node, which can then be used for filtering results from certain catalog endpoints. See the [`-node-meta` command-line flag](#_node_meta) for more information.

  ```json
  {
    "node_meta": {
      "instance_type": "t2.medium"
    }
  }
  ```

- `performance` Available in Consul 0.7 and later, this is a nested object that allows tuning the performance of different subsystems in Consul. See the [Server Performance](/docs/install/performance) documentation for more details. The following parameters are available:

  - `leave_drain_time` - A duration that a server will dwell during a graceful leave in order to allow requests to be retried against other Consul servers. Under normal circumstances, this can prevent clients from experiencing "no leader" errors when performing a rolling update of the Consul servers. This was added in Consul 1.0. Must be a duration value such as 10s. Defaults to 5s.

  - `raft_multiplier` - An integer multiplier used by Consul servers to scale key Raft timing parameters. Omitting this value or setting it to 0 uses default timing described below. Lower values are used to tighten timing and increase sensitivity while higher values relax timings and reduce sensitivity. Tuning this affects the time it takes Consul to detect leader failures and to perform leader elections, at the expense of requiring more network and CPU resources for better performance.

    By default, Consul will use a lower-performance timing that's suitable
    for [minimal Consul servers](/docs/install/performance#minimum), currently equivalent
    to setting this to a value of 5 (this default may be changed in future versions of Consul,
    depending if the target minimum server profile changes). Setting this to a value of 1 will
    configure Raft to its highest-performance mode, equivalent to the default timing of Consul
    prior to 0.7, and is recommended for [production Consul servers](/docs/install/performance#production).

    See the note on [last contact](/docs/install/performance#production-server-requirements) timing for more
    details on tuning this parameter. The maximum allowed value is 10.

  - `rpc_hold_timeout` - A duration that a client
    or server will retry internal RPC requests during leader elections. Under normal
    circumstances, this can prevent clients from experiencing "no leader" errors.
    This was added in Consul 1.0. Must be a duration value such as 10s. Defaults
    to 7s.

- `ports` This is a nested object that allows setting the bind ports for the following keys:

  - `dns` ((#dns_port)) - The DNS server, -1 to disable. Default 8600.
    TCP and UDP.
  - `http` ((#http_port)) - The HTTP API, -1 to disable. Default 8500.
    TCP only.
  - `https` ((#https_port)) - The HTTPS API, -1 to disable. Default -1
    (disabled). **We recommend using `8501`** for `https` by convention as some tooling
    will work automatically with this.
  - `grpc` ((#grpc_port)) - The gRPC API, -1 to disable. Default -1 (disabled).
    **We recommend using `8502`** for `grpc` by convention as some tooling will work
    automatically with this. This is set to `8502` by default when the agent runs
    in `-dev` mode. Currently gRPC is only used to expose Envoy xDS API to Envoy
    proxies.
  - `serf_lan` ((#serf_lan_port)) - The Serf LAN port. Default 8301. TCP
    and UDP.
  - `serf_wan` ((#serf_wan_port)) - The Serf WAN port. Default 8302. Set
    to -1 to disable. **Note**: this will disable WAN federation which is not recommended.
    Various catalog and WAN related endpoints will return errors or empty results.
    TCP and UDP.
  - `server` ((#server_rpc_port)) - Server RPC address. Default 8300. TCP
    only.
  - `sidecar_min_port` ((#sidecar_min_port)) - Inclusive minimum port number
    to use for automatically assigned [sidecar service registrations](/docs/connect/registration/sidecar-service).
    Default 21000. Set to `0` to disable automatic port assignment.
  - `sidecar_max_port` ((#sidecar_max_port)) - Inclusive maximum port number
    to use for automatically assigned [sidecar service registrations](/docs/connect/registration/sidecar-service).
    Default 21255. Set to `0` to disable automatic port assignment.
  - `expose_min_port` ((#expose_min_port)) - Inclusive minimum port number
    to use for automatically assigned [exposed check listeners](/docs/connect/registration/service-registration#expose-paths-configuration-reference).
    Default 21500. Set to `0` to disable automatic port assignment.
  - `expose_max_port` ((#expose_max_port)) - Inclusive maximum port number
    to use for automatically assigned [exposed check listeners](/docs/connect/registration/service-registration#expose-paths-configuration-reference).
    Default 21755. Set to `0` to disable automatic port assignment.

- `primary_datacenter` - This designates the datacenter
  which is authoritative for ACL information, intentions and is the root Certificate
  Authority for Connect. It must be provided to enable ACLs. All servers and datacenters
  must agree on the primary datacenter. Setting it on the servers is all you need
  for cluster-level enforcement, but for the APIs to forward properly from the clients,
  it must be set on them too. In Consul 0.8 and later, this also enables agent-level
  enforcement of ACLs.

- `primary_gateways` Equivalent to the [`-primary-gateway`
  command-line flag](#_primary_gateway). Takes a list of addresses to use as the
  mesh gateways for the primary datacenter when authoritative replicated catalog
  data is not present. Discovery happens every [`primary_gateways_interval`](#primary_gateways_interval)
  until at least one primary mesh gateway is discovered. This was added in Consul
  1.8.0.

- `primary_gateways_interval` Time to wait
  between [`primary_gateways`](#primary_gateways) discovery attempts. Defaults to
  30s. This was added in Consul 1.8.0.

- `protocol` ((#protocol)) Equivalent to the [`-protocol` command-line
  flag](#_protocol).

- `raft_protocol` ((#raft_protocol)) Equivalent to the [`-raft-protocol`
  command-line flag](#_raft_protocol).

- `raft_snapshot_threshold` ((#\_raft_snapshot_threshold)) This controls
  the minimum number of raft commit entries between snapshots that are saved to disk.
  This is a low-level parameter that should rarely need to be changed. Very busy
  clusters experiencing excessive disk IO may increase this value to reduce disk
  IO, and minimize the chances of all servers taking snapshots at the same time.
  Increasing this trades off disk IO for disk space since the log will grow much
  larger and the space in the raft.db file can't be reclaimed till the next snapshot.
  Servers may take longer to recover from crashes or failover if this is increased
  significantly as more logs will need to be replayed. In Consul 1.1.0 and later
  this defaults to 16384, and in prior versions it was set to 8192.

- `raft_snapshot_interval` ((#\_raft_snapshot_interval)) This controls how often servers check if they
  need to save a snapshot to disk. This is a low-level parameter that should rarely need to be changed. Very busy clusters experiencing excessive disk IO may increase this value to reduce disk IO, and minimize the chances of all servers taking snapshots at the same time. Increasing this trades
  off disk IO for disk space since the log will grow much larger and the space in the raft.db file can't be reclaimed till the next snapshot. Servers may take longer to recover from crashes or failover if this is increased significantly as more logs will need to be replayed. In Consul 1.1.0 and later this defaults to `30s`, and in prior versions it was set to `5s`.

- `raft_trailing_logs` - This controls how many
  log entries are left in the log store on disk after a snapshot is made. This should
  only be adjusted when followers cannot catch up to the leader due to a very large
  snapshot size that and high write throughput causing log truncation before an snapshot
  can be fully installed. If you need to use this to recover a cluster, consider
  reducing write throughput or the amount of data stored on Consul as it is likely
  under a load it is not designed to handle. The default value is 10000 which is
  suitable for all normal workloads. Added in Consul 1.5.3.

- `reap` This controls Consul's automatic reaping of child processes,
  which is useful if Consul is running as PID 1 in a Docker container. If this isn't
  specified, then Consul will automatically reap child processes if it detects it
  is running as PID 1. If this is set to true or false, then it controls reaping
  regardless of Consul's PID (forces reaping on or off, respectively). This option
  was removed in Consul 0.7.1. For later versions of Consul, you will need to reap
  processes using a wrapper, please see the [Consul Docker image entry point script](https://github.com/hashicorp/docker-consul/blob/master/0.X/docker-entrypoint.sh)
  for an example. If you are using Docker 1.13.0 or later, you can use the new `--init`
  option of the `docker run` command and docker will enable an init process with
  PID 1 that reaps child processes for the container. More info on [Docker docs](https://docs.docker.com/engine/reference/commandline/run/#options).

- `reconnect_timeout` This controls how long it
  takes for a failed node to be completely removed from the cluster. This defaults
  to 72 hours and it is recommended that this is set to at least double the maximum
  expected recoverable outage time for a node or network partition. WARNING: Setting
  this time too low could cause Consul servers to be removed from quorum during an
  extended node failure or partition, which could complicate recovery of the cluster.
  The value is a time with a unit suffix, which can be "s", "m", "h" for seconds,
  minutes, or hours. The value must be >= 8 hours.

- `reconnect_timeout_wan` This is the WAN equivalent
  of the [`reconnect_timeout`](#reconnect_timeout) parameter, which controls
  how long it takes for a failed server to be completely removed from the WAN pool.
  This also defaults to 72 hours, and must be >= 8 hours.

- `recursors` This flag provides addresses of upstream DNS
  servers that are used to recursively resolve queries if they are not inside the
  service domain for Consul. For example, a node can use Consul directly as a DNS
  server, and if the record is outside of the "consul." domain, the query will be
  resolved upstream. As of Consul 1.0.1 recursors can be provided as IP addresses
  or as go-sockaddr templates. IP addresses are resolved in order, and duplicates
  are ignored.

- `rejoin_after_leave` Equivalent to the [`-rejoin` command-line flag](#_rejoin).

- `retry_join` - Equivalent to the [`-retry-join`](#retry-join) command-line flag.

- `retry_interval` Equivalent to the [`-retry-interval` command-line flag](#_retry_interval).

- `retry_join_wan` Equivalent to the [`-retry-join-wan` command-line flag](#_retry_join_wan). Takes a list of addresses to attempt joining to WAN every [`retry_interval_wan`](#_retry_interval_wan) until at least one join works.

- `retry_interval_wan` Equivalent to the [`-retry-interval-wan` command-line flag](#_retry_interval_wan).

- `segment` <EnterpriseAlert inline /> - Equivalent to the [`-segment` command-line flag](#_segment).

- `segments` <EnterpriseAlert inline /> - This is a list of nested objects
  that allows setting the bind/advertise information for network segments. This can
  only be set on servers. Review the [Network Segments tutorial](https://learn.hashicorp.com/tutorials/consul/network-partition-datacenters)
  for more details.

  - `name` ((#segment_name)) - The name of the segment. Must be a string
    between 1 and 64 characters in length.
  - `bind` ((#segment_bind)) - The bind address to use for the segment's
    gossip layer. Defaults to the [`-bind`](#_bind) value if not provided.
  - `port` ((#segment_port)) - The port to use for the segment's gossip
    layer (required).
  - `advertise` ((#segment_advertise)) - The advertise address to use for
    the segment's gossip layer. Defaults to the [`-advertise`](#_advertise) value
    if not provided.
  - `rpc_listener` ((#segment_rpc_listener)) - If true, a separate RPC
    listener will be started on this segment's [`-bind`](#_bind) address on the rpc
    port. Only valid if the segment's bind address differs from the [`-bind`](#_bind)
    address. Defaults to false.

- `server` Equivalent to the [`-server` command-line flag](#_server).

- `non_voting_server` - Equivalent to the [`-non-voting-server` command-line flag](#_non_voting_server).

- `server_name` When provided, this overrides the [`node_name`](#_node)
  for the TLS certificate. It can be used to ensure that the certificate name matches
  the hostname we declare.

- `session_ttl_min` The minimum allowed session TTL. This ensures sessions are not created with TTL's
  shorter than the specified limit. It is recommended to keep this limit at or above
  the default to encourage clients to send infrequent heartbeats. Defaults to 10s.

- `skip_leave_on_interrupt` This is similar
  to [`leave_on_terminate`](#leave_on_terminate) but only affects interrupt handling.
  When Consul receives an interrupt signal (such as hitting Control-C in a terminal),
  Consul will gracefully leave the cluster. Setting this to `true` disables that
  behavior. The default behavior for this feature varies based on whether or not
  the agent is running as a client or a server (prior to Consul 0.7 the default value
  was unconditionally set to `false`). On agents in client-mode, this defaults to
  `false` and for agents in server-mode, this defaults to `true` (i.e. Ctrl-C on
  a server will keep the server in the cluster and therefore quorum, and Ctrl-C on
  a client will gracefully leave).

- `start_join` An array of strings specifying addresses
  of nodes to [`-join`](#_join) upon startup. Note that using
  `retry_join` could be more appropriate to help mitigate
  node startup race conditions when automating a Consul cluster deployment.

- `start_join_wan` An array of strings specifying addresses
  of WAN nodes to [`-join-wan`](#_join_wan) upon startup.

- `telemetry` This is a nested object that configures where
  Consul sends its runtime telemetry, and contains the following keys:

  - `circonus_api_token` ((#telemetry-circonus_api_token)) A valid API
    Token used to create/manage check. If provided, metric management is
    enabled.

  - `circonus_api_app` ((#telemetry-circonus_api_app)) A valid app name
    associated with the API token. By default, this is set to "consul".

  - `circonus_api_url` ((#telemetry-circonus_api_url))
    The base URL to use for contacting the Circonus API. By default, this is set
    to "https://api.circonus.com/v2".

  - `circonus_submission_interval` ((#telemetry-circonus_submission_interval)) The interval at which metrics are submitted to Circonus. By default, this is set to "10s" (ten seconds).

  - `circonus_submission_url` ((#telemetry-circonus_submission_url))
    The `check.config.submission_url` field, of a Check API object, from a previously
    created HTTPTRAP check.

  - `circonus_check_id` ((#telemetry-circonus_check_id))
    The Check ID (not **check bundle**) from a previously created HTTPTRAP check.
    The numeric portion of the `check._cid` field in the Check API object.

  - `circonus_check_force_metric_activation` ((#telemetry-circonus_check_force_metric_activation)) Force activation of metrics which already exist and are not currently active.
    If check management is enabled, the default behavior is to add new metrics as
    they are encountered. If the metric already exists in the check, it will **not**
    be activated. This setting overrides that behavior. By default, this is set to
    false.

  - `circonus_check_instance_id` ((#telemetry-circonus_check_instance_id)) Uniquely identifies the metrics coming from this **instance**. It can be used to
    maintain metric continuity with transient or ephemeral instances as they move
    around within an infrastructure. By default, this is set to hostname:application
    name (e.g. "host123:consul").

  - `circonus_check_search_tag` ((#telemetry-circonus_check_search_tag)) A special tag which, when coupled with the instance id, helps to narrow down
    the search results when neither a Submission URL or Check ID is provided. By
    default, this is set to service:application name (e.g. "service:consul").

  - `circonus_check_display_name` ((#telemetry-circonus_check_display_name)) Specifies a name to give a check when it is created. This name is displayed in
    the Circonus UI Checks list. Available in Consul 0.7.2 and later.

  - `circonus_check_tags` ((#telemetry-circonus_check_tags))
    Comma separated list of additional tags to add to a check when it is created.
    Available in Consul 0.7.2 and later.

  - `circonus_broker_id` ((#telemetry-circonus_broker_id))
    The ID of a specific Circonus Broker to use when creating a new check. The numeric
    portion of `broker._cid` field in a Broker API object. If metric management is
    enabled and neither a Submission URL nor Check ID is provided, an attempt will
    be made to search for an existing check using Instance ID and Search Tag. If
    one is not found, a new HTTPTRAP check will be created. By default, this is not
    used and a random Enterprise Broker is selected, or the default Circonus Public
    Broker.

  - `circonus_broker_select_tag` ((#telemetry-circonus_broker_select_tag)) A special tag which will be used to select a Circonus Broker when a Broker ID
    is not provided. The best use of this is to as a hint for which broker should
    be used based on **where** this particular instance is running (e.g. a specific
    geo location or datacenter, dc:sfo). By default, this is left blank and not used.

  - `disable_hostname` ((#telemetry-disable_hostname))
    This controls whether or not to prepend runtime telemetry with the machine's
    hostname, defaults to false.

  - `dogstatsd_addr` ((#telemetry-dogstatsd_addr)) This provides the address
    of a DogStatsD instance in the format `host:port`. DogStatsD is a protocol-compatible
    flavor of statsd, with the added ability to decorate metrics with tags and event
    information. If provided, Consul will send various telemetry information to that
    instance for aggregation. This can be used to capture runtime information.

  - `dogstatsd_tags` ((#telemetry-dogstatsd_tags)) This provides a list
    of global tags that will be added to all telemetry packets sent to DogStatsD.
    It is a list of strings, where each string looks like "my_tag_name:my_tag_value".

  - `filter_default` ((#telemetry-filter_default))
    This controls whether to allow metrics that have not been specified by the filter.
    Defaults to `true`, which will allow all metrics when no filters are provided.
    When set to `false` with no filters, no metrics will be sent.

  - `metrics_prefix` ((#telemetry-metrics_prefix))
    The prefix used while writing all telemetry data. By default, this is set to
    "consul". This was added in Consul 1.0. For previous versions of Consul, use
    the config option `statsite_prefix` in this same structure. This was renamed
    in Consul 1.0 since this prefix applied to all telemetry providers, not just
    statsite.

  - `prefix_filter` ((#telemetry-prefix_filter))
    This is a list of filter rules to apply for allowing/blocking metrics by
    prefix in the following format:

    ```json
    ["+consul.raft.apply", "-consul.http", "+consul.http.GET"]
    ```

    A leading "**+**" will enable any metrics with the given prefix, and a leading "**-**" will block them. If there is overlap between two rules, the more specific rule will take precedence. Blocking will take priority if the same prefix is listed multiple times.

  - `prometheus_retention_time` ((#telemetry-prometheus_retention_time)) If the value is greater than `0s` (the default), this enables [Prometheus](https://prometheus.io/)
    export of metrics. The duration can be expressed using the duration semantics
    and will aggregates all counters for the duration specified (it might have an
    impact on Consul's memory usage). A good value for this parameter is at least
    2 times the interval of scrape of Prometheus, but you might also put a very high
    retention time such as a few days (for instance 744h to enable retention to 31
    days). Fetching the metrics using prometheus can then be performed using the
    [`/v1/agent/metrics?format=prometheus`](/api/agent#view-metrics) endpoint.
    The format is compatible natively with prometheus. When running in this mode,
    it is recommended to also enable the option [`disable_hostname`](#telemetry-disable_hostname)
    to avoid having prefixed metrics with hostname. Consul does not use the default
    Prometheus path, so Prometheus must be configured as follows. Note that using
    ?format=prometheus in the path won't work as ? will be escaped, so it must be
    specified as a parameter.

    ```yaml
    metrics_path: '/v1/agent/metrics'
    params:
      format: ['prometheus']
    ```

  - `statsd_address` ((#telemetry-statsd_address)) This provides the address
    of a statsd instance in the format `host:port`. If provided, Consul will send
    various telemetry information to that instance for aggregation. This can be used
    to capture runtime information. This sends UDP packets only and can be used with
    statsd or statsite.

  - `statsite_address` ((#telemetry-statsite_address)) This provides the
    address of a statsite instance in the format `host:port`. If provided, Consul
    will stream various telemetry information to that instance for aggregation. This
    can be used to capture runtime information. This streams via TCP and can only
    be used with statsite.

- `syslog_facility` When [`enable_syslog`](#enable_syslog)
  is provided, this controls to which facility messages are sent. By default, `LOCAL0`
  will be used.

- `tls_min_version` Added in Consul 0.7.4, this specifies
  the minimum supported version of TLS. Accepted values are "tls10", "tls11", "tls12",
  or "tls13". This defaults to "tls12". WARNING: TLS 1.1 and lower are generally
  considered less secure; avoid using these if possible.

- `tls_cipher_suites` Added in Consul 0.8.2, this specifies the list of
  supported ciphersuites as a comma-separated-list. The list of all supported
  ciphersuites is available through
  [this search](https://github.com/hashicorp/consul/search?q=cipherMap+%3A%3D+map&unscoped_q=cipherMap+%3A%3D+map).

- `tls_prefer_server_cipher_suites` Added in Consul 0.8.2, this
  will cause Consul to prefer the server's ciphersuite over the client ciphersuites.

- `translate_wan_addrs` If set to true, Consul
  will prefer a node's configured [WAN address](#_advertise-wan)
  when servicing DNS and HTTP requests for a node in a remote datacenter. This allows
  the node to be reached within its own datacenter using its local address, and reached
  from other datacenters using its WAN address, which is useful in hybrid setups
  with mixed networks. This is disabled by default.

  Starting in Consul 0.7 and later, node addresses in responses to HTTP requests will also prefer a
  node's configured [WAN address](#_advertise-wan) when querying for a node in a remote
  datacenter. An [`X-Consul-Translate-Addresses`](/api#translated-addresses) header
  will be present on all responses when translation is enabled to help clients know that the addresses
  may be translated. The `TaggedAddresses` field in responses also have a `lan` address for clients that
  need knowledge of that address, regardless of translation.

  The following endpoints translate addresses:

  - [`/v1/catalog/nodes`](/api/catalog#list-nodes)
  - [`/v1/catalog/node/<node>`](/api/catalog#retrieve-map-of-services-for-a-node)
  - [`/v1/catalog/service/<service>`](/api/catalog#list-nodes-for-service)
  - [`/v1/health/service/<service>`](/api/health#list-nodes-for-service)
  - [`/v1/query/<query or name>/execute`](/api/query#execute-prepared-query)

- `ui` - Equivalent to the [`-ui`](#_ui) command-line flag.

- `ui_dir` - Equivalent to the [`-ui-dir`](#_ui_dir) command-line
  flag. This configuration key is not required as of Consul version 0.7.0 and later.
  Specifying this configuration key will enable the web UI. There is no need to specify
  both ui-dir and ui. Specifying both will result in an error.

- `unix_sockets` - This allows tuning the ownership and
  permissions of the Unix domain socket files created by Consul. Domain sockets are
  only used if the HTTP address is configured with the `unix://` prefix.

  It is important to note that this option may have different effects on
  different operating systems. Linux generally observes socket file permissions
  while many BSD variants ignore permissions on the socket file itself. It is
  important to test this feature on your specific distribution. This feature is
  currently not functional on Windows hosts.

  The following options are valid within this construct and apply globally to all
  sockets created by Consul:

  - `user` - The name or ID of the user who will own the socket file.
  - `group` - The group ID ownership of the socket file. This option
    currently only supports numeric IDs.
  - `mode` - The permission bits to set on the file.

- `verify_incoming` - If set to true, Consul
  requires that all incoming connections make use of TLS and that the client
  provides a certificate signed by a Certificate Authority from the
  [`ca_file`](#ca_file) or [`ca_path`](#ca_path). This applies to both server
  RPC and to the HTTPS API. By default, this is false, and Consul will not
  enforce the use of TLS or verify a client's authenticity. Turning on
  `verify_incoming` on consul clients protects the HTTPS endpoint, by ensuring
  that the certificate that is presented by a 3rd party tool to the HTTPS
  endpoint was created by the CA that the consul client was setup with. If the
  UI is served, the same checks are performed.

- `verify_incoming_rpc` - If set to true, Consul
  requires that all incoming RPC connections make use of TLS and that the client
  provides a certificate signed by a Certificate Authority from the [`ca_file`](#ca_file)
  or [`ca_path`](#ca_path). By default, this is false, and Consul will not enforce
  the use of TLS or verify a client's authenticity.

- `verify_incoming_https` - If set to true,
  Consul requires that all incoming HTTPS connections make use of TLS and that the
  client provides a certificate signed by a Certificate Authority from the [`ca_file`](#ca_file)
  or [`ca_path`](#ca_path). By default, this is false, and Consul will not enforce
  the use of TLS or verify a client's authenticity. To enable the HTTPS API, you
  must define an HTTPS port via the [`ports`](#ports) configuration. By default,
  HTTPS is disabled.

- `verify_outgoing` - If set to true, Consul requires
  that all outgoing connections from this agent make use of TLS and that the server
  provides a certificate that is signed by a Certificate Authority from the [`ca_file`](#ca_file)
  or [`ca_path`](#ca_path). By default, this is false, and Consul will not make use
  of TLS for outgoing connections. This applies to clients and servers as both will
  make outgoing connections.

  ~> **Security Note:** Note that servers that specify `verify_outgoing = true` will always talk to other servers over TLS, but they still _accept_
  non-TLS connections to allow for a transition of all clients to TLS.
  Currently the only way to enforce that no client can communicate with a
  server unencrypted is to also enable `verify_incoming` which requires client
  certificates too.

- `verify_server_hostname` - If set to true,
  Consul verifies for all outgoing TLS connections that the TLS certificate
  presented by the servers matches `server.<datacenter>.<domain>`
  hostname. By default, this is false, and Consul does not verify the hostname
  of the certificate, only that it is signed by a trusted CA. This setting is
  _critical_ to prevent a compromised client from being restarted as a server
  and having all cluster state _including all ACL tokens and Connect CA root keys_
  replicated to it. This is new in 0.5.1.

  ~> **Security Note:** From versions 0.5.1 to 1.4.0, due to a bug, setting
  this flag alone _does not_ imply `verify_outgoing` and leaves client to server
  and server to server RPCs unencrypted despite the documentation stating otherwise. See
  [CVE-2018-19653](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-19653)
  for more details. For those versions you **must also set `verify_outgoing = true`** to ensure encrypted RPC connections.

- `watches` - Watches is a list of watch specifications which
  allow an external process to be automatically invoked when a particular data view
  is updated. See the [watch documentation](/docs/agent/watches) for more detail.
  Watches can be modified when the configuration is reloaded.

## Ports Used

Consul requires up to 6 different ports to work properly, some on
TCP, UDP, or both protocols.

Review the [required ports](/docs/install/ports) table for a list of
required ports and their default settings.

## Reloadable Configuration

Reloading configuration does not reload all configuration items. The
items which are reloaded include:

- ACL Tokens
- [Configuration Entry Bootstrap](#config_entries_bootstrap)
- Checks
- [Discard Check Output](#discard_check_output)
- HTTP Client Address
- Log level
- [Metric Prefix Filter](#telemetry-prefix_filter)
- [Node Metadata](#node_meta)
- [RPC rate limiting](#limits)
- [HTTP Maximum Connections per Client](#http_max_conns_per_client)
- Services
- TLS Configuration
  - Please be aware that this is currently limited to reload a configuration that is already TLS enabled. You cannot enable or disable TLS only with reloading.
- Watches
