The fifth factor of the 12-factor app manifesto is "build, release, run". It says that
the release stage takes the build produced by the build stage and combines it with the deploy's current config. The resulting release contains both the build and the config...
The third factor "Config" explains that the configuration is stored in environment variables. It sounds like a contradiction to me.
If the config is stored in environment variables, how can it be contained in the release? A docker file is the only possibility I could think of, but this would be specific to Docker.