I don’t have statistics as it was used in my lab at home which I have recently torn down and begun rebuilding (new servers, new hypervisor and not enough of a crap given to v2v the VM’s I had instead of reinstalling).

From memory though, MongoDB didn’t use much since it mostly stored configuration for Graylog, the Graylog processes themselves took up a couple hundred MB and elasticsearch ate up everything I allowed it to (typical behavior of a database though).

I didn’t bother tweaking any of the settings and just relied on memory pressure of the VM everything ran on to limit resource usage, if you’re keeping lots of history and need fast access to it then obviously you’d need to give ES more RAM to work with.

Thanks for sharing -- I wasn't aware that Graylog only used mongo for the configuration information -- sounds like they're using it as a synchronization option... Wonder if they're working on any alternatives like etcd or even kubernetes-native synchronization options... After a little looking it looks like the answer is "no" (https://community.graylog.org/t/will-mongodb-ever-be-replace...)