def announce(key, port, opts={}, &block)
      payload = [key,port]
      link.send 'announce', payload, opts, &block
      if config.auto_announce
        periodically(config.auto_announce_interval) do
          link.send 'announce', payload, opts, &block
        end
      end
    end
def announce(key, port, opts={}, &block)
      payload = [key,port]
      link.send 'announce', payload, opts, &block
      if config.auto_announce
        periodically(config.auto_announce_interval) do
          link.send 'announce', payload, opts, &block
        end
      end
    end
Announce a specific service `key` available on specific `port`
 passed block is called when the announce is sent
 @param key [string] service identifier
 @param port [int] service port number
 @block callback