title: Graylog connecting to existing elasticsearch shows 503
body: <ul>
  <li>Graylog v4.0.7</li>
  <li>ElasticSearch v7.7</li>
  <li>MongoDb v4.4</li>
  </ul>
  <p>We are setting up Graylog in our kubernetes cluster. Graylog can connect to MongoDB server from another cluster using LB. When we connect our Graylog to ElasticSearch which is in different cluster (using LB e.g. <a href="https://myelastic.sample.com:443" rel="nofollow noreferrer">https://myelastic.sample.com:443</a>), logs from the app shows 503. But when we curl some elasticsearch api it shows 200.</p>
  <p>This only occurs in graylog pod.</p>
  <pre><code>Caused by: org.graylog.shaded.elasticsearch7.org.elasticsearch.client.ResponseException: method [GET], host [https://myelastic.sample.com:443], URI [/_alias/graylog_deflector?ignore_throttled=false&amp;ignore_unavailable=false&amp;expand_wildcards=open%2Cclosed&amp;allow_no_indices=true], status line [HTTP/1.1 503 Service Unavailable]
  upstream connect error or disconnect/reset before headers. reset reason: connection failure
      at org.graylog.shaded.elasticsearch7.org.elasticsearch.client.RestClient.convertResponse(RestClient.java:302) ~[?:?]
      at org.graylog.shaded.elasticsearch7.org.elasticsearch.client.RestClient.performRequest(RestClient.java:272) ~[?:?]
      at org.graylog.shaded.elasticsearch7.org.elasticsearch.client.RestClient.performRequest(RestClient.java:246) ~[?:?]
  </code></pre>