title: questions about socket.io adapters
body: <p>I am currently working on a node.js-based <a href="http://socket.io/" rel="nofollow">socket.io</a> service that makes use of the <a href="https://nodejs.org/api/cluster.html" rel="nofollow">node.js cluster module</a> to spawn several node.js processen on the same machine.</p>
  
  <p>The socket.io docs say that it is required to use an <a href="http://socket.io/docs/using-multiple-nodes/#passing-events-between-nodes" rel="nofollow">adapter</a> if multiple processes are used, so that e.g. broadcasting targets not only the clients connected to the current process, but to all connected clients of every process.</p>
  
  <ol>
  <li>Do I understand it correctly, that I am required to use such an adapter even if all processes are spawned locally (i.e. not across several servers)?</li>
  <li>The server processes need to communicate from time to time (just unidirectional, i.e. broadcast a message without the need for a response). If such an adapter is in use (e.g. <a href="https://github.com/socketio/socket.io-redis" rel="nofollow">socket.io-redis</a>), can I use it to broadcast to all server processes as well? Or are the adapters only used to target connected clients?</li>
  </ol>