One of the main plugins we were using with our 2.x Elasticsearch cluster was KOPF. This plugin was a web interface to the Elasticsearch API and it was an easy way of performing common tasks on our Elasticsearch cluster.
When we upgraded our Elasticsearch cluster to version 5.x, we could not continue using this plugin because it was not longer supported. The good thing was that the author of KOPF, Leonardo Menezes, had a new project called "CEREBRO" to offer an alternative to KOPF when running Elasticsearch 5.x.