Dockerfile stages must have a command

In multi-stage Dockerfile, you have to be careful for what stages you run. Want to avoid having misteriously exit 0 errors in containers? Add a CMD at the end of the Dockerfile stage with some dummy command like

CMD ["/bin/bash", "echo", "Command for stage X"]

Any stage that has no command will exit without informing the user of what happened. This could cause some mysterious errors if you are getting up all containers and not overwritting the command of the ones that have none.

Conclusion

A good way of making sure you are not exiting early while being oblivious of what is happening is setting a dummy command for each stage in a multi-stage Dockerfile.