title: The scope of Firebase Instance Id and Token
body: <p>I've read a lot of articles about <code>Firebase Instance Id</code> and <code>registration token</code> <a href="https://firebase.google.com/docs/reference/android/com/google/firebase/iid/FirebaseInstanceId" rel="noreferrer">here</a>, <a href="https://developers.google.com/instance-id/" rel="noreferrer">here</a> and <a href="https://firebase.google.com/docs/android/setup" rel="noreferrer">here</a>.</p>
  
  <p>I have some confusions about their <strong>scope and relationship</strong> between <code>Instance Id</code> and <code>Token</code>. I would like to validate that my understandings are correct or wrong.</p>
  
  <ol>
  <li><code>Instance Id</code> is generated per <strong>App</strong>. Not per <strong>installed device</strong>. For example, if you have Mail app and Notes App, you will have <strong>two</strong> Instance Id on firebase.</li>
  <li><code>Token</code> is generated per installed devices. For example, if you have <strong>ten</strong> users installing your app, you will have <strong>ten</strong> registration tokens.</li>
  <li>One <code>Instance Id</code> will have many registration tokens.</li>
  <li>Normally, we only have to keep <code>registration tokens</code> (not Instance Id) on our App Server to send <strong>push notifications</strong>.</li>
  </ol>