You’ll want to make sure you have the proper plugin version to go along with the Elasticsearch version and Couchbase version you’re using. Because of the way Elasticsearch manages plugin security, you can’t just use the highest release of the plugin, you actually need to look at the chart pretty carefully.
Consult the version compatibility matrix here:
You need to know your exact ES version and then you can determine which plugin version you need. For example, if you are running ES version 2.2.x, you need the Elasticsearch transport plugin version 2.2.2.x, where x may be missing. You also need to edit your security policy as directed in the readme on the github repo. It’s easy to make a small mistake with the security config, so be sure to check your steps over carefully.