DNSSRVCluster

Elixir clustering with DNS SRV records.

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Installation

The package can be installed by adding dns_srv_cluster to your list of dependencies in mix.exs:

def deps do
  [
    {:dns_srv_cluster, "~> 0.2.0"}
  ]
end

Add to your DNS zone your SRV record (https://en.wikipedia.org/wiki/SRV_record):

_app._tcp.yourdomain.com. 60 IN SRV 0 10 1234 node1.yourdomain.com.
_app._tcp.yourdomain.com. 60 IN SRV 0 10 1234 node2.yourdomain.com.
_app._tcp.yourdomain.com. 60 IN SRV 0 10 1234 node3.yourdomain.com.
_app._tcp.yourdomain.com. 60 IN SRV 0 10 1234 node4.yourdomain.com.

Add to your config files (config/prod.exs, config/dev.exs):

config :dns_srv_cluster,
  query: "_app._tcp.yourdomain.com"

Add this to your rel/env.sh.eex:

export RELEASE_DISTRIBUTION="${RELEASE_DISTRIBUTION:-"name"}"
export RELEASE_NODE="${RELEASE_NODE:-"<%= @release.name %>"}"

By default, nodes from the same release will have the same cookie. If you want different applications or releases to connect to each other, then you must set the RELEASE_COOKIE, either in your deployment platform or inside rel/env.sh.eex:

export RELEASE_COOKIE="my-app-cookie"

Configuration options

• query - your DNS SRV record, for example: "_app._tcp.yourdomain.com".
• interval - the millisec interval between DNS queries. Defaults to 5_000.
• connect_timeout - the millisec timeout to allow discovered nodes to connect. Defaults to 10_000.

If you want it in your supervision tree

Do in mix.exs:

def deps do
  [
    {:dns_srv_cluster, "~> 0.2.0", runtime: false}
  ]
end

runtime: false will block application from starting.

And use DNSSRVCluster.Worker as a child:

children = [
  {DNSSRVCluster.Worker, query: "_app._tcp.yourdomain.com"}
]

{:ok, pid} = Supervisor.start_link(children, strategy: :one_for_one)

Support Matrix

Tests automatically run against a matrix of OTP and Elixir Versions, see the ci.yml for details.

OTP \ Elixir	1.12	1.13	1.14	1.15	1.16
24	✅	✅	✅	✅	✅
25	N/A	✅	✅	✅	✅
26	N/A	N/A	✅	✅	✅

Documentation

Documentation can be found at https://hexdocs.pm/dns_srv_cluster.