One best practice when running a container is to launch the process with a non root user. This is usually done through the usage of the USER instruction in the Dockerfile. But, if this instruction is not present it doesn’t necessary mean the process is run as root.
By default, root in a container is the same root (uid 0) as on the host machine. If a user manages to break out of an application running as root in a container, he may be able to gain access to the host with the same root user. This access would be ever easier to gain if the container was run with incorrect flags or with bind mouts of host folders in R/W.
Running a MongoDB container
If you do not it yet, I highly recommend to give Play With Docker a try.
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