In the ES docs I saw that the logstash connects to ES over HTTP.
https://www.elastic.co/guide/en/logstash/current/plugins-outputs-elasticsearch.html
This output only speaks the HTTP protocol. HTTP is the preferred protocol for interacting with Elasticsearch as of Logstash 2.0. We strongly encourage the use of HTTP over the node protocol for a number of reasons.
Is it possible to connect the ES over HTTPS???