In addition to what mvg and warkolm mentioned, we do expect quite a few people to use Watcher to monitor Elasticsearch health and proactively notify the administrator if issues occur.
Today, Marvel is a great way to monitor Elasticsearch over time - it tracks many cluster health and performance metrics over time. We are planning a tighter integration between Marvel and Watcher over time, but for now, we have started providing recipes for creating watches based on Marvel data:
https://www.elastic.co/guide/en/watcher/current/watching-marvel-data.html