The Secrets of Docker Secrets

Most web apps need login information of some kind, and it is a bad idea to put them in your source code where it gets saved to a git repository that everyone can see. Usually these are handled by environment variables, but Docker has come up with what they call Docker secrets. The idea is deceptively simple in retrospect. While you figure it out it is arcane and difficult to parse what is going on.

Essentially the secrets function create in memory files in the docker image that contain the secret data. The data can come from files, or a Docker swarm.

The first thing to know is that the application running in the docker image needs to be written to take advantage of the Docker secrets function. Instead of getting the password from an environment variable, it would get the password from the file system at /run/secrets/secretname. Not all images available use this functionality. If they don't describe how to use Docker secrets, the won't work. The files will be created in the image, but the application won't read them.

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