I am a big fan of the ELK stack and use it daily for various parts of my job. All of the logs from my physical systems, VMs and containers get funneled into elasticsearch, indexed and are available for me to slice and dice with Kibana. In addition to syslog data I also like to funnel the systemd journal into elasticsearch. This is easily accomplished by changing the journald.conf ForwardToSyslog configuration directive to yes:
sed -i.bak 's/#ForwardToSyslog/ForwardToSyslog\=yes/'
This small change will cause all journal entries to get routed to the local syslog daemon. Once they are there you can set up your favorite log shipping solution to get them into your elasticsearch cluster.