elasticsearch transport-couchbase plugin refusing connection on port 9091
If you can't telnet or browse to port 9091, this most likely indicates a network config issue. The plugin binds to the interface that elasticsearch binds to. The first thing to check is that the bind_host and publish_host in elasticsearch.yml is configured to bind to an interface that allows connections from wherever the proxy is located and that the proxy is really connecting on that interface.
There is a thread in github for the bug in transport plugin where it might not bind to all interfaces : https://github.com/couchbaselabs/elasticsearch-transport-couchbase/issues/134
The above solutions didn't work for me, however I added this line:-Djava.net.preferIPv4Stack=trueto /etc/elasticsearch/jvm.options and it seemed fixed the issue in my case