args in marathon file does not resolve env variables

[triggity]

cmd field in a marathon app config would resolve environment variables before passing them in. this is documented here: https://mesosphere.github.io/marathon/docs/ports.html

however, the args field does not have it's environment variables resolved before passing in.
Is this a bug or deliberate and missing from the documentation?

a canonical example:

using a basic image with

ENTRYPOINT ["echo"]

and args: [ "$PORT0"]

the container logs show it echoing
$PORT0 instead of the expected resolved env variable for $PORT0

[aquamatthias]

Hey @triggity the args are passed directly to the exec syscall without running a shell. This is intended behavior. If you need env expansion please use cmd instead of args

[micahhausler]

@aquamatthias So is it impossible to pass a command to a docker container and have an environment variable be interpreted in that command? cmd is incompatible with a container in an app definition.

[aquamatthias]

@micahhausler Don't know what you mean by incompatible. Please see https://mesosphere.github.io/marathon/docs/native-docker.html, especially the Command vs Args section.

[micahhausler]

I see what you mean now. I got confused because the cmd doesn't respect the docker container's entrypoint.