NAME

    gdnsd-plugin-weighted - gdnsd plugin implementing "weighted" records

SYNOPSIS

    Example plugin config:

      plugins => {
        weighted => {
          multi = false # default
          service_types = none
          up_thresh => 0.5 # default
          corpwww => {
            lb01 = [ lb01.example.com., 99 ]
            lb02 = [ lb02.example.com., 15 ]
            lb03 = [ lb03, 1 ]
          }
          frontwww6 => {
            service_types = up
            multi = true
            wwwhost01 = [ 2001:db8::123, 4 ]
            wwwhost02 = [ 2001:db8::456, 1 ]
            wwwhost03 = [ 2001:db8::789, 2 ]
          }
          pubwww => {
            service_types = [ web_check, foo ]
            up_thresh => 0.01,
            pubhost01 = [ 192.0.2.1, 44 ]
            pubhost02 = [ 192.0.2.2, 11 ]
            pubhost02 = [ 192.0.2.3, 11 ]
            pubhost02 = [ 192.0.2.4, 11 ]
          }
          cdnwww => {
            service_types = web_check
            datacenter1 => {
              d1-lb1 = [ 127.0.0.1, 2 ]
              d1-lb2 = [ 127.0.0.2, 2 ]
            }
            datacenter2 => {
              d2-lb1 = [ 127.0.0.3, 2 ]
              d2-lb2 = [ 127.0.0.4, 2 ]
              d2-lb3 = [ 127.0.0.5, 1 ]
            }
          }
          mixed => {
            multi => false,
            addrs_v4 => {
              lb1 = [ 127.0.0.3, 2 ]
              lb2 = [ 127.0.0.4, 2 ]
            }
            addrs_v6 => {
              multi => true
              www6set1 = {
                lb01 => [ 2001:db8::123, 4 ]
                lb02 => [ 2001:db8::456, 1 ]
              }
              www6set2 = {
                lb01 => [ 2001:db8::789, 4 ]
                lb02 => [ 2001:db8::ABC, 1 ]
              }
            }
          }
          cn => {
            cnames => {
              foo = [ lb01.example.com., 99 ]
              bar = [ lb02.example.com., 15 ]
            }
          }
        }
      }

    Zonefile RRs referencing the above:

      www.corp   300 DYNC weighted!corpwww
      www6.front 300 DYNA weighted!frontwww6
      www        300 DYNA weighted!pubwww
      cdn        300 DYNA weighted!cdnwww
      mixed-a    300 DYNA weighted!mixed
      cnames     300 DYNC weighted!cn

DESCRIPTION

    gdnsd-plugin-weighted can be used to return one (or a subset) of several
    address records, or one of several CNAME records based on
    dynamic-weighted probabilities.

CONFIGURATION - TOP LEVEL

    At the top level, there are three special parameter keys:
    "service_types", "up_thresh", and "multi". These only affect the
    behavior of address ("DYNA") lookups. They are ignored for CNAME
    ("DYNC") lookups. All of these keys are inherited and override-able at
    the per-resource and per-address-family levels.

    The top-level default "service_types" is "default", which is a built-in
    service type provided by gdnsd. For more information about configuring
    non-default service type's, see the main gdnsd.config(5) documentation.
    The default polls the "/" URL at each IP address on port 80 for a "200
    OK" response every 10 seconds, and has some anti-flap parameters that
    stabilize the state against isolated, intermittent failures.

    "multi" is a boolean that can be "true" or "false", and defaults to
    "false". "multi" controls the behavior of the algorithm for selecting
    result addresses, discussed in detail later.

    "up_thresh" defines a floating point fraction of summed address weights
    in the range "(0.0 - 1.0]", defaulting to 0.5, and is used to influence
    failure/failover behavior.

    Other than those three, the rest of the top level keys are the names of
    your resources, and their values are the configuration of each resource.

CONFIGURATION - PER-RESOURCE

    Inside a given resource's configuration hash, again the three
    address-related parameters "services_types", "multi", and "up_thresh"
    may be specified to override their settings per-resource.

    There are two basic configuration modes within a resource:

    1) Explicit per-family/type sub-stanzas. In this mode, the resource
    contains one or more of the keys "addrs_v4", "addrs_v6", and "cnames".
    "addrs_v4" and/or "addrs_v6" can both be specified in the same resource,
    but "cnames" cannot co-exist with either of the other two.

    The contents of each stanza configure response RRs of the given type for
    this resource, and in the addrs_v4/addrs_v6 cases, the 3 behavioral
    parameters "service_types", "multi", and "up_thresh" can be overridden
    per-address-family as well.

    2) Automatic top-level detection of just one family/type. In this mode,
    you can configure the top-level of a resource with valid contents for
    one of the stanzas "addrs_v4", "addrs_v6", or "cnames", and the
    family/type will be autodetected, and be the only type available in this
    resource.

CONFIGURATION - CNAMES

    When configuring cnames, the value of each item should be "[ CNAME,
    WEIGHT ]", and the resource will be useful for "DYNC" zonefile records,
    resolving to a weighted CNAME record in responses. The weighting
    decision will return a single CNAME answer, with the probability of each
    choice being "weight / total_weight".

    If the CNAMEs are not fully-qualified (do not end in "."), the current
    $ORIGIN value for the zonefile RR being queried will be appended to
    complete the name, much as you would expect if the same
    not-fully-qualified name were substituted into the zonefiles everywhere
    the relevant DYNC record exists.

CONFIGURATION - ADDRESSES

    With the exception that "addrs_v4" and "addrs_v6" must contain only
    addresses of the correct family (or in the top-level auto-detect case,
    the top level entries must all be of the same family), the two stanzas
    behave identically. When both are present, they are both used in every
    "DYNA" response (as gdnsd always includes opposite-family records in the
    Additional section of A/AAAA queries).

    Within either address family type, there are two different binary
    dimensions (multi -> true/false, and grouped-vs-ungrouped) upon which
    the configuration and behavior hinge, leading to four different possible
    cases: ungrouped-single, ungrouped-multi, grouped-single, and
    grouped-multi. Each will be discussed in detail below:

THE UNGROUPED SINGLE CASE

    This is the simplest case. The code detects this case when it sees that
    "multi" is false (the default), and that the values of the keys are
    arrays rather than sub-hashes. Each hash key is an address label, and
    each value is an array of "[ IPADDR, WEIGHT ]".

    When answering a query in this case, first the weights are converted to
    dynamic weights. The dynamic weight of an address is its configured
    weight if the monitored state is "UP" or "DANGER", or zero if the
    monitored state is "DOWN". The dynamic weights are summed to produce a
    dynamic weight total, and then a single address to respond with is
    chosen from the set, with each address having the odds
    "addr_dynamic_weight / total_dynamic_weight".

    However, if the "total_dynamic_weight" is less than "ceil(up_thresh *
    total_configured_weight)", then the dynamic weights are all reset to
    their configured full values so that the response odds are the same as
    if all were "UP", and resource-level failure is signalled to any
    upper-layer meta-plugin (e.g. metafo or geoip) when applicable.

    Example (X could be a whole resource, or an addrs_v4 stanza):

      X => {
        multi => false # default
        # odds below assume no addresses are down:
        lb01 => [ 192.0.2.1, 45 ] # 25% chance (45/180)
        lb02 => [ 192.0.2.1, 60 ] # 33% chance (60/180)
        lb03 => [ 192.0.2.1, 75 ] # 42% chance (75/180)
      }

THE UNGROUPED MULTI CASE

    This case is detected when, (as above) the values of the keys are arrays
    of "[ IPADDR, WEIGHT]", but the parameter "multi" is true. The change
    from the above behavior is primarily that multiple addresses from the
    weighted set can be returned in each response. The "maximum", rather
    than the sum, of the dynamic weights (again, zero for down addresses,
    configured-weight otherwise), is found, and the odds of each address's
    inclusion in the response set is "addr_dyanmic_weight /
    max_dynamic_weight".

    This means all non-"DOWN" addresses which share the group's maximum
    dynamic weight value will always be included, whereas others will be
    optionally included depending on the odds. At least one address is
    always returned (because logically, at least one address has the maximum
    weight, giving it a 100% chance), and sometimes the full non-"DOWN" set
    will be returned.

    "up_thresh" behaves as in the previous case: If the sum of the dynamic
    weight values is less than "ceil(up_thresh * total_configured_weight)",
    then the dynamic weights are all set to their configured values and the
    result set is calculated as if all were "UP", while signalling
    resource-level failure to upstream meta-plugins (geoip or metafo).

    Example:

      X => {
        multi => true
        # odds below assume no addresses are down:
        lb01 => [ 192.0.2.1, 45 ] # 75% chance (45/60)
        lb02 => [ 192.0.2.1, 60 ] # 100% chance (60/60)
        lb03 => [ 192.0.2.1, 60 ] # 100% chance (60/60)
        # overall possible result-sets:
        # lb01,lb02,lb03 -> 75%
        # lb02,lb03 -> 25%
      }

THE GROUPED SINGLE CASE

    The grouped cases are detected when the keys' values are sub-hashes at
    the outer level rather than arrays of "[ IPADDR, WEIGHT]". In the
    grouped case, first the set is divided into named groups, and then
    within each group individual addresses are configured as "addrlabel => [
    IPADDR, WEIGHT ]".

    Example:

       X => {
         group1 => {
           lb01 => [ 192.0.2.1, 10 ]
           lb02 => [ 192.0.2.1, 20 ]
           lb03 => [ 192.0.2.1, 30 ]
         }
         group2 => {
           lb01 => [ 192.0.2.7, 10 ]
           lb02 => [ 192.0.2.8, 20 ]
           lb03 => [ 192.0.2.9, 30 ]
         }
       }

    The grouped single case, of course, occurs when the configuration layout
    is as shown above, and the "multi" parameter is "false" (the default).

    In grouped-single mode, essentially the groups are weighted against each
    other similarly to the single case for ungrouped addresses, resulting in
    the choice of a single group from the set of groups. Then the addresses
    within the chosen group are weighted against each other in multi-style,
    returning potentially more than one address from the chosen group.

    Specifically, each group's odds of being the single group chosen is
    "group_dyn_weight / total_dyn_weight", where the group's dynamic weight
    is the sum of the dynamic weights within it ("DOWN" addresses are zero),
    and the total dynamic weight is the dynamic sum of all groups. Then
    within each group, the odds of each address being included in the
    multi-response set is "addr_dyn_weight / group_max_dyn_weight".

    "up_thresh" operates on all groups as a whole, and if the non-"DOWN" sum
    of all weights in all groups fails to meet the standard of
    "ceil(up_thresh * total_sum_configured_weight)", then all addresses will
    be treated as if they are "UP" for selection purposes, and
    resource-level failure will be signalled upstream.

THE GROUPED MULTI CASE

    You can probably infer this one's behavior from reading about the
    previous three cases. The difference from the previous grouped-single
    case is that the multi-vs-single behaviors are reversed. Multiple groups
    are chosen based on the dynamic maximum weight between the groups, and a
    single weighted address is returned from the subset within each chosen
    group. All of the details above logically apply in the way you would
    expect, as all of these four cases internally share the same code and
    logic, they just apply different bits of it to different subsets of the
    problem.

GENERAL NOTES ON ADDRESS MODE CASES ABOVE

    Note that any time multi-selection is in effect at a layer (the top
    layer when multi is true, or within a group when when multi is false),
    the minimum count of chosen items will be the count of items that share
    the maximum weight within the set. e.g. a set of items with weights "30,
    30, 30, 20, 20" will always choose at least 3/5 items (because the first
    three have 100% odds of inclusion), and the total response set will
    range as high as all 5 items with some probability.

    A practical use-case example for grouped-single:

    Splitting groups on subnet boundaries in grouped-single mode gives the
    result that a single response packet never mixes subnets. This would
    enable your DNS-based balancing to defeat certain forms of client-level
    Destination Address Selection interference, while still returning
    multiple addresses per response (all from one subnet).

    A practical use-case for grouped-multi:

    Suppose you have a large set of addresses which can be logically grouped
    into subsets that have some shared failure risk (e.g. subpartitions of a
    datacenter which share infrastructure). With grouped-multi behavior,
    clients will get up to N (count of groups) addresses in a round-robin
    response, but a given response set will never contain two addresses from
    the same group/subset. This maximizes the chance that the client can
    successfully fail over to another address in the list when its primary
    selection fails, since the total set in each response does not share any
    per-subset failure mode.

LIMITS

    All weights must be positive integer values greater than zero and less
    than 2^20 (1048576).

    There is a limit of 64 addresses, address-groups, or cnames at the top
    level of a resource (or per address family in the addrs_v4/addrs_v6
    cases), and a limit of 64 addresses within each address group in the
    grouped modes.

SEE ALSO

    gdnsd.config(5), gdnsd.zonefile(5), gdnsd(8)

    The gdnsd manual.

COPYRIGHT AND LICENSE

    Copyright (c) 2012 Anton Tolchanov <me@knyar.net>, Brandon L Black
    <blblack@gmail.com> and Jay Reitz <jreitz@gmail.com>

    This file is part of gdnsd-plugin-weighted.

    gdnsd-plugin-weighted is free software: you can redistribute it and/or
    modify it under the terms of the GNU General Public License as published
    by the Free Software Foundation, either version 3 of the License, or (at
    your option) any later version.

    gdnsd-plugin-weighted is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
    Public License for more details.

    You should have received a copy of the GNU General Public License along
    with gdnsd-plugin-weighted. If not, see <http://www.gnu.org/licenses/>.

