Any recommendations for open source server / application monitoring?

Type of server? Stats wanted? We need basic info mate

Good point, Ubuntu. Im looking for something sort of application/server monitoring software. Basically want to monitor application log (PHP errors, response time, HTTP requests, etc) and as well as the infrastructure (services, firewalls, logs, usage etc)

I just implemented a couple of weeks ago ELK stack.
use kibana for ui( you can show logs filter and searchable, and also you can make some pretty sick visualisations.
use elasticsesrch as the data source for kibana. warning it might take some ram.
use logstash to parse / filter / manipulate logs and insert in elastic search.
use filebeat for watching logs file and send new logs into logstash.

i put each service inside a docker container and working pretty well.