No way to make the exec line dynamic

[fgabolde]

I'm using Tiller to set up a web application's config files.

The app expects the number of HTTP workers to be provided as a command-line argument, there is no way to provide it as an environment variable or in a config file. E.g:

exec: ["carton", "exec", "plackup", "-Ilib", "-s", "Starman", "--workers", "5", "--port", "5000", "--env", "production", "bin/app.psgi"]

starts the app with 5 workers. I'd like to specify this number via an environment variable instead, e.g.:

docker run --env WORKERS=10 myapp:latest

I have not found any way to do this in the documentation. Looking at the source code I don't think I can do anything like ["--workers", $WORKERS] but I am not a Ruby developers so might have missed something.