About a year ago I set up an ES cluster to load Apache logs into as an experiment. Around a month later my boss asked if it was down. "Yeah, it looks like it, since you are using it let me upgrade it from an experiment to critical!" Since then we've been using it in more and more places, and are looking to see if it would be a good fit for storing some of our user data in. The big barrier right now is that we are running the version of SQLServer right before changed data capture became part of the standard edition, and that's the way we'd probably prefer to synchronize data into ES from our primary database. We have a couple home grown solutions to synchronizing secondary data sources, and we'd like to get out of that business. The SQL server is always going to be our source of truth, probably.