I found Keen actually really interesting. You can analyse whatever you can push into your account. You can bulk load past information. It's actually a pretty interesting platform. I think the worst thing it does is web analytics, it does custom analytics of whatever data you are working on pretty well though. I've been using it to capture webhook information. I had to write a custom interface, it doesn't handle them natively, but it was pretty easy using php, then later nodejs.
I've used it to capture specific events out of fail2ban, syslog, and specific app events. You can correlate them just like you are using ELK stack.
The pricing structure will make it prohibitive to toss all infrastructure events into it, but if you are looking to simply measure and create metrics for a few things, this thing is pretty cool.
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