Quotes from James Turnbull

A union mount is a mount that allows several filesystems to be mounted at one time but appear to be one filesystem. The union mount overlays the filesystems on top of one another so that the resulting filesystem may contain files and subdirectories from any or all of the underlying filesystems.

There's also a great post from the Datadog team on visualizing time series data that is worth reading.

If you need to run multiple processes or commands as part of starting a container you should use a service management tool like Supervisor.

This reduces the risk of "worked in dev, now an ops problem.