Enable GELF driver on Docker engine

You can send all container logs to Graylog by changing the docker engine logging driver

$ sudo vim /usr/lib/systemd/system/docker.service
ExecStart=/usr/bin/docker daemon -H fd:// 
      --log-driver=gelf 
      --log-opt gelf-address=udp://10.10.10.1:12202 

Restart Docker

$ sudo systemctl daemon-reload
$ sudo systemctl restart docker