Merge branch 'mention-plugins-in-es-troubleshooting' into 'master'

Mention plugins in troubleshooting Elasticsearch integration

See merge request gitlab-org/gitlab!48108

doc/integration/elasticsearch.md

@@ -929,6 +929,13 @@ Gitlab::Elastic::Indexer::Error: time="2020-01-23T09:13:00Z" level=fatal msg="he
 You probably have not used either `http://` or `https://` as part of your value in the **"URL"** field of the Elasticsearch Integration Menu. Please make sure you are using either `http://` or `https://` in this field as the [Elasticsearch client for Go](https://github.com/olivere/elastic) that we are using [needs the prefix for the URL to be accepted as valid](https://github.com/olivere/elastic/commit/a80af35aa41856dc2c986204e2b64eab81ccac3a).
 Once you have corrected the formatting of the URL, delete the index (via the [dedicated Rake task](#gitlab-advanced-search-rake-tasks)) and [reindex the content of your instance](#enabling-advanced-search).
 
+### My Elasticsearch cluster has a plugin and the integration is not working
+
+Certain 3rd party plugins may introduce bugs in your cluster or for whatever
+reason may be incompatible with our integration. You should try disabling
+plugins so you can rule out the possibility that the plugin is causing the
+problem.
+
 ### Low-level troubleshooting
 
 There is a [more structured, lower-level troubleshooting document](../administration/troubleshooting/elasticsearch.md) for when you experience other issues, including poor performance.