Yes, I think it is. But i just want to clarify for those doing the same type of install, you have to expose the ports on the mattermost app container to the docker network, but also have to use the -p (publish option) to publish the ports so that the host OS can see them. Not mentioned anywhere that I saw and very difficult to guess. You can edit your docker-compose.yml file to do this each time the container is created:
Ports:
- "8000:8000"