Document few low-level details related to Docker executor (CMD and ENTRYPOINT problem, DinD usage)
Recently, while investigating user's problem, we've discussed with @dblessing about how Runner uses Docker images, and especially how Runner executes scripts in the job container, and how
CMD are used here. No documentation that would help to understand how things work is one of the problems that are frequently occuring in users reports.
Another problem, related to Docker executor, that frequently gets back to us is how volumes mounting works when Docker-in-Docker is use (the
The two above should be finally documented.