Join RabbitMQ to cluster via Consul

join-rabbitmq-cluster.rb

#!/usr/bin/env ruby
require 'json'
require 'net/http'
require 'optparse'
require 'ostruct'

options = OpenStruct.new
options.service_name = "rabbitmq"
options.port = 8500

OptionParser.new { |opts|
  opts.banner = "Usage: join-rabbitmq-cluster.rb [options]"

  opts.on("-s", "--service NAME", "Name of the RabbitMQ service") do |name|
    options.service_name = name
  end

  opts.on("-p", "--port PORT", "Consul HTTP API port") do |port|
    options.port = port
  end

  opts.on_tail("-h", "--help", "Show this message") do
    puts opts
    exit
  end
}.parse!

begin
  uri = URI("http://localhost:#{options.port}/v1/health/service/#{options.service_name}")
  nodes = JSON.load(Net::HTTP.get(uri))
rescue => error
  $stderr.puts "Could not retrieve health information for service"
  $stderr.puts error
  exit 1
end

nodes.reject! do |node|
  node['Checks'].none? do |check|
    check['ServiceID'] == options.service_name && check['Status'] == 'passing'
  end
end

if nodes.empty?
  $stderr.puts "Could not locate node providing suitable \"#{options.service_name}\" service"
  exit 2
end

node = nodes.sample['Node']

puts "Using node \"#{node['Node']}\" to provide \"#{options.service_name}\" service"

if `rabbitmqctl cluster_status`.include?(node['Node'])
  puts "RabbitMQ already belongs to the cluster"
  exit 0
end

unless `host #{node['Node']}`
  $stderr.puts "Could not resolve node #{node['Node']} with DNS"
  exit 3
end

system "rabbitmqctl stop_app"
system "rabbitmqctl join_cluster --ram rabbit@#{node['Node']}"
system "rabbitmqctl start_app"

system "rabbitmqctl cluster_status"

RabbitMQ is configured by default to use the short hostname, not the FQDN, of cluster nodes. This means that RabbitMQ must be able to resolve rabbit1, for instance. You can either use your own DNS set the search domain OR you can setup dnsmasq to forward to Consul's DNS interface with the search domain node.dc1.consul.

Note that changing RabbitMQ to use FQDN requires changing the files in /usr/lib/rabbitmq/bin to use the -name flag instead of -sname.