title: Elasticsearch 7.9 CCR changing the number of replicas on the leader index is not replicated by the follower index
body: <p>I have an issue/question</p>
  <p>I have 2 es clusters. Cross cluster replication is configured.
  After reading replication mechanism from <a href="https://www.elastic.co/guide/en/elasticsearch/reference/7.x/xpack-ccr.html" rel="nofollow noreferrer">documentation</a> I still have few questions.</p>
  <ol>
  <li>What is the &quot;<strong>some updates</strong>&quot; in below quote? And what is &quot;<strong>as needed</strong>&quot;??? This is no clear.</li>
  </ol>
  <blockquote>
  <p>The follower index automatically retrieves some updates applied to the leader index, while other updates are retrieved as needed</p>
  </blockquote>
  <ol start="2">
  <li>Right after this I see another quote from which I can't understand how I can change replicas on leader so as it will replicated on follower? Is it possible at all?</li>
  </ol>
  <blockquote>
  <p>For example, changing the number of replicas on the leader index is not replicated by the follower index, so that setting might not be retrieved.</p>
  </blockquote>
  <ol start="3">
  <li>Next quote. How I can understand what is the static and what is the dynamic properties.</li>
  </ol>
  <blockquote>
  <p>If you apply a non-dynamic settings change to the leader index that is
  needed by the follower index, the follower index closes itself,
  applies the settings update, and then re-opens itself. The follower
  index is unavailable for reads and cannot replicate writes during this
  cycle.</p>
  </blockquote>
  <ol start="4">
  <li>Num_of_replicas is it non-dynamic property? If yes why it is not updating it at the follower site as said in previous quote. And how I could get list of such not updatable parameters.</li>
  </ol>