Worth mentioning that Elastic.co has a commercial product called Watcher [1] which I think is a really nice way for making an automated alert system. The downside is being a commercial product I can't use Watcher and would have to implement one myself.

I am still deciding between ES, a relational database and Cassandra for time series data. We use graphite now and are happy with it, but I think having a single database handling logs, events and metrics data would be much more ideal. Having logs already in ES does make ES a better choice.

[1]: https://www.elastic.co/guide/en/watcher/current/index.html