Syslog driver not working with docker compose and elk stack
You need to use tcp://127.0.0.1:514 instead of tcp://elk-custom:514. Reason being this address is being used by docker and not by the container. That is why elk-custom is not reachable.
So this will only work when you map the port (which you have done) and the elk-service is started first (which you have done) and the IP is reachable from the docker host, for which you would use tcp://127.0.0.1:514