Provided by: gdnsd_1.11.1-1_amd64 
NAME
gdnsd-plugin-multifo - gdnsd plugin for multi-address, all-active failover groups
SYNOPSIS
Example plugin config:
plugins => {
multifo => {
up_thresh => 0.3
service_types => default,
v4www => {
lb01 => 192.0.2.200,
lb02 => 192.0.2.201,
lb03 => 192.0.2.202,
}
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, default ],
addrs_v4 => [ 192.0.2.100, 192.0.2.101, 192.0.2.102 ]
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
DESCRIPTION
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.
TOP-LEVEL PLUGIN CONFIG
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.
RESOURCE CONFIG
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-family):
up_thresh
Floating point, default 0.5, range (0.0 - 1.0]. This configures the per-resource "up_thresh"
threshold. More details in "UP THRESH" below.
service_types
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.
SHORTCUT CONFIG
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 => [ 192.0.2.1, 192.0.2.2 ] }
res1 => { addrs_v4 => { 1 => 192.0.2.1, 2 => 192.0.2.2 } }
OPERATIONAL MECHANICS
All of the addresses for all of the resources are monitored using the per-address-family inherited
"service_types" specified (default would be simple HTTP/1.0 monitoring for "200 OK" on port 80). 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 or even DANGER 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:
UP THRESH
Any non-DOWN address is considered an acceptable result for up_thresh purposes, even ones in the
transitional DANGER state. If there are not "enough" non-DOWN 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 geoip.
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
SEE ALSO
gdnsd.config(5), gdnsd.zonefile(5), gdnsd(8), gdnsd-plugin-simplefo(8)
The gdnsd manual.
COPYRIGHT AND LICENSE
Copyright (c) 2012 Brandon L Black <blblack@gmail.com>
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
<http://www.gnu.org/licenses/>.
gdnsd 1.11.1 2013-11-05 GDNSD-PLUGIN-MULTIFO(8)