AWSの"Role"タグからデプロイ対象のサーバを取得

deploy.rb

# config/deploy.rb
def tagged_servers(tag_key, tag_value, default=[])
  @ec2 ||= AWS::EC2.new(ec2_endpoint: 'ec2.ap-northeast-1.amazonaws.com')
  ret = @ec2.instances.map do |instance|
    next if instance.tags[tag_key] != tag_value
    next if instance.status != :running
    instance.dns_name.empty? ? instance.ip_address : instance.dns_name
  end.compact
  return default if ret.empty?
  ret
end

def tag(tag_value, *args)
  AWS.memoize {
    tagged_servers(tag_key, tag_value).each do |host|
      server(host, *args)
    end
  }
end

# config/deploy/environment.rb
tag 'app', :web, :app