Provided by: gdnsd_2.2.0-1ubuntu1_i386 bug


       gdnsd-plugin-multifo - gdnsd plugin for multi-address, all-active
       failover groups


       Example plugin config:

         plugins => {
           multifo => {
             up_thresh => 0.3
             service_types => up,
             v4www => {
               lb01 =>,
               lb02 =>,
               lb03 =>,
             v6smtp => {
               service_types => [ smtp ],
               up_thresh => 0.1,
               lb01_v6 => 2001:DB8::1,
               lb02_v6 => 2001:DB8::2,
               lb03_v6 => 2001:DB8::3,
             pubwww => {
               up_thresh => 0.5
               service_types => corpwww_type
               addrs_v4 => [,, ]
               addrs_v6 => {
                 service_types => [ up ],
                 up_thresh => 0.7
                 lb01_v6 => 2001:DB8::1,
                 lb02_v6 => 2001:DB8::2,
                 lb03_v6 => 2001:DB8::3,

       Example zonefile RRs:

         web4 180 DYNA multifo!v4www
         smtp 180 DYNA multifo!v6smtp
         www 180 DYNA multifo!pubwww


       gdnsd-plugin-multifo is designed to do multi-address all-active
       failover grouping.  Basically, for each configured resource name, you
       supply a labeled list of addresses.  multifo monitors these addresses
       according to "service_types", and answers "DYNA" address queries using
       the non-"DOWN" subset.  The core gdnsd code will round-robin rotate the
       records on the way out, as it does for all address RR-sets.


       At the top level of the plugin's configuration stanza, two special
       parameters "up_thresh" and "service_types" are supported. These set
       default per-resource options of the same name for any resources which
       do not define them explicitly.

       The rest of the hash entries at the top level are the names of the
       resources you define.  Each resource gets a configuration hash of its
       own for containing resource-specific parameters as well as the actual
       address data.


       Within a resource, you have two basic options.  You can either directly
       specify a set of "label => address" pairs which are all the same family
       (IPv4 or IPv6), or you can use the sub-stanzas "addrs_v4" and/or
       "addrs_v6" to specify one or both families in the same resource.

       The "up_thresh" and "service_types" parameters are inherited through
       every level, and can be overridden at any level (even per-address-

           Floating point, default 0.5, range (0.0 - 1.0].  This configures
           the per-resource "up_thresh" threshold.  More details in "UP
           THRESH" below.

           Array of strings, or single string.  Default "default".  This sets
           the monitored service_types for this resource.  If an array of more
           than one is provided, all will be monitored for each address, and
           the net monitored state will be the minimum (worst) of the set.
           See gdnsd.config(8) for more details on service_types.


       If you have no parameters (service_types, up_thresh) to configure in a
       given stanza (single-family direct resource config, or addrs_v[46]),
       and do not care about the descriptive per-address labels used in
       monitoring, you can replace the hash with an array of addresses.  The
       labels will be generated for you as a series of integers starting with
       1.  For example, the following are equivalent:

          res1 => { addrs_v4 => [, ] }
          res1 => { addrs_v4 => { 1 =>, 2 => } }


       All of the addresses for all of the resources are monitored using the
       per-address-family inherited "service_types" specified (default would
       be the static virtual monitor "up").  When the core daemon requests a
       lookup for address records of a given family on one of this plugin's
       resources, it goes through essentially the following process to
       determine the set of response addresses for that address family: 1) Add
       all non-DOWN addresses to the result set.  2) If the set of non-DOWN
       addresses fail the up_thresh check, add *all* addresses to the result
       set as a fallback.  3) If any address is in the DOWN state, cut the
       zonefile-specified TTL in half

       This process is repeated independently for each of the IPv4 and IPv6
       address subsets, in the case that a resource has both address families
       configured (the TTL is only cut in half once of course).  Details on
       the up_thresh check follow:


       If there are not enough UP addresses to pass the threshold (per address
       family), all addresses (of a given address family) will be returned as
       a fallback.

       The threshold is implemented mathematically as in the following pseudo-
       code "if(non_down >= ceil(thresh * total)) threshold_passed;".  For
       example, if thresh is at the default value of 0.5, and there are 3
       total IPv4 addresses, then 2 of them must be non-down to pass the
       threshold.  The net result is that with the default threshold, the
       plugin will never return an isolated single address from a set of 3.
       It will either return all 3, or it will return 2/3 if a single address
       from the set has failed.

       When the threshold check fails (and all addresses are returned) for
       either address family, resource-level total failure will also be
       signaled to any applicable upstream meta-plugins such as metafo or

       General rules for the results of the up_thresh formula:

       ·   A threshold of 1.0 will only pass if all addresses are not-down.
           This is mostly pointless, you might as well not monitor anything
           and set up these addresses as a static set in a zonefile.

       ·   A threshold of 0.01 will pass even if only one address is alive and
           return just that one address, even if it's e.g. the only one left
           out of 40.

       ·   Because a threshold of 0.0 is illegal, if all addresses are down
           the threshold will always fail, returning all addresses.

       Intermediate value examples: (threshold: non-down/total required to
       pass threshold):

       ·   0.1: 1/1 1/2 1/3 1/4 1/5 1/6 1/7 1/8 2/16

       ·   0.2: 1/1 1/2 1/3 1/4 1/5 2/6 2/7 2/8 4/16

       ·   0.3: 1/1 1/2 1/3 2/4 2/5 2/6 3/7 3/8 5/16

       ·   0.4: 1/1 1/2 2/3 2/4 2/5 3/6 3/7 4/8 7/16

       ·   0.5: 1/1 1/2 2/3 2/4 3/5 3/6 4/7 4/8 8/16

       ·   0.6: 1/1 2/2 2/3 3/4 3/5 4/6 5/7 5/8 10/16

       ·   0.7: 1/1 2/2 3/3 3/4 4/5 5/6 5/7 6/8 12/16

       ·   0.8: 1/1 2/2 3/3 4/4 4/5 5/6 6/7 7/8 13/16

       ·   0.9: 1/1 2/2 3/3 4/4 5/5 6/6 7/7 8/8 15/16


       gdnsd.config(5), gdnsd.zonefile(5), gdnsd(8), gdnsd-plugin-simplefo(8)

       The gdnsd manual.


       Copyright (c) 2012 Brandon L Black <>

       This file is part of gdnsd.

       gdnsd 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 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.  If not, see <>.