title: What is a correct update endpoint for communication between elastic.v7 client and Elasticsearch 6.x server?
body: <p>I am currently getting backwards incompatibility issue when hitting endpoint of <code>/update</code> using elastic.v7 as client to Elasticsearch 6.x server.
  I noticed that for update, the 7.x endpoint is <code>POST /&lt;index&gt;/_update/&lt;_id&gt;</code>, while the 6.x is expecting <code>POST /&lt;index&gt;/_doc/&lt;_id&gt;/_update</code>.</p>
  <p>This results in that when I make update operation from v7 client to 6.x Elasticsearch server, I am seeing the error below</p>
  <pre><code>{&quot;error&quot;:{&quot;root_cause&quot;:[{&quot;type&quot;:&quot;invalid_type_name_exception&quot;,&quot;reason&quot;:&quot;Document mapping type name can't start with '_', found: [_update]&quot;}],&quot;type&quot;:&quot;invalid_type_name_exception&quot;,&quot;reason&quot;:&quot;Document mapping type name can't start with '_', found: [_update]&quot;},&quot;status&quot;:400}
  </code></pre>
  <p>I found this difference when I enabled client side tracelog.</p>
  <h3>Version of Elasticsearch used</h3>
  <p>elastic.v7 as client (Elasticsearch 6.x server as a way to test backwards compatibility)</p>
  <h3>Expected behavior</h3>
  <p>Successful update with <code>POST /&lt;index&gt;/_update/&lt;_id&gt;</code> from v7 client to both Elasticsearch 6.x and 7.x servers.</p>
  <h3>Actual behavior</h3>
  <p>Error described above with <code>POST /&lt;index&gt;/_update/&lt;_id&gt;</code> endpoint from v7 client to Elasticsearch 6.x server.</p>
  <h3>Steps to reproduce the behavior</h3>
  <ol>
  <li>Spin up a ES 6 server</li>
  <li>Use elastic v7 as client</li>
  <li>Create an index</li>
  <li>Insert a document</li>
  <li>Update the document with <code>POST /&lt;index&gt;/_update/&lt;_id&gt;</code> endpoint from elastic.v7</li>
  </ol>
  <p>Is this a suggestion of not to use v7 client for 6.x server? Originally I am thinking of sticking this plan as it would be easier to use one client to request to both Elasticsearch servers (v6 and v7).</p>