Docker Network
When you work with multiple docker containers that are not in the same compose file, the issue is that each is in a different network. However, there is a useful docker command to add an existing container to an existing network:
docker network connect [OPTIONS] NETWORK CONTAINER
An example would be to add a container named mycontainer to the network mynetwork:
docker network connect mynetwork mycontainer
Beside that there are two more useful commands in docker network:
First one displays all network controllers in Docker:
docker network ls
And the second one displays details of a Docker network:
docker network inspect mynetwork