Merge branch 'docs_vlad_es_no_node_available' into 'master'

Added no ES node available in troubleshooting

See merge request gitlab-org/gitlab!23760

doc/integration/elasticsearch.md

@@ -611,6 +611,15 @@ Here are some common pitfalls and how to overcome them:
     }
   }'
   ```
+  
+- **I'm getting a `health check timeout: no Elasticsearch node available` error in Sidekiq during the indexing process**
+
+   ```
+   Gitlab::Elastic::Indexer::Error: time="2020-01-23T09:13:00Z" level=fatal msg="health check timeout: no Elasticsearch node available"
+   ```
+
+   You probably have not used either `http://` or `https://` as part of your value in the **"URL"** field of the Elasticseach 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 acceped as valid](https://github.com/olivere/elastic/commit/a80af35aa41856dc2c986204e2b64eab81ccac3a).
+   Once you have corrected the formatting of the URL please delete the index (via the [dedicated rake task](#gitlab-elasticsearch-rake-tasks)) and [index the content of your intance](#adding-gitlabs-data-to-the-elasticsearch-index) once more.
 
 ### Reverting to basic search