Capistrano config helper to retrieve automatically retrieve running instances to deploy

deploy.rb

# deploy.rb
def retrieve_instances(name_prefix)
  require 'aws-sdk'
  next_token = nil
  dns_list = []
  begin
    resp = Aws::EC2::Client.new.describe_instances(
      filters: [{name: "tag:private:service", values: ['my-service']}],
      next_token: next_token)
    resp.reservations.each do |r|
      r.instances.each do |i|
        if i.tags.find { |t| t.key == 'Name' }.value.start_with?(name_prefix)
          dns_list << i.network_interfaces.first.association.public_dns_name
        end
      end
    end
  end while (next_token = resp.next_token)
  dns_list.sort.map { |d| "app@#{d}" }
end

set :ssh_options, {
  forward_agent: true,
  auth_methods: %w(publickey)
}.tap { |opt|
  if ENV['CAPISTRANO_USE_SSH_PROXY']
    require 'net/ssh/proxy/command'
    opt[:proxy] = Net::SSH::Proxy::Command.new('ssh -W %h:%p example.com')
  end
}

# for each stages
hosts = retrieve_instances('app001')
role :app, hosts
role :web, hosts
role :db,  [hosts.first]