Logstash is an excellent way to eat up logs and send them elsewhere. In a typical setup you’ll send them to Elasticsearch and the excellent Kibana for viewing and analysis, which works well but is missing a vital part: being alerted when your application throws errors.
There’s a whole bunch of ways you can deal with errors without Logstash, one of which is Sentry. This is a software service which takes your errors, samples and groups them and, crucially, alerts you by email (or many other options). Sentry can plug in to most applications with its different Raven clients, which will allow you to track errors as part of your application and then send them to Sentry directly.
But, well, if you’re already using Logstash to log everything (including errors), wouldn’t it be great to just have Logstash send errors on to Sentry for you? I think so! And, luckily, it’s quick and easy to do!