Auto-configuring dynamic containers

We can't always execute a binary to get what we want. A configuration done dynamically is a very common situation; system paths can be dynamic, users and passwords can be auto-generated, network ports can be contextual, third-party credentials will be different in development and in production, slaves will join their masters, cluster members will find other nodes, and most other similar changing elements will need to adapt at runtime. The trick here is to combine environment variables with the use of a script as an entry point that will be executed no matter what, and behave according to the environment variables, optionally combined with a command from the Dockerfile.

Getting ready

To step through this recipe, you will need a working Docker installation.

How to do it…

Our objective is to create a temporary, dynamic SSH server in a Docker container, with credentials we can't know in advance. So, to make it work as intended, we'll want to execute this container...