Practical usage documentation

[viraptor]

When using the secrets with the buildkite docker plugin, the secrets are not automatically propagated. Specifically:

    plugins:
      - docker#v3.11.0:
          image: "..."
          propagate_environment: true

will not use the secrets. Instead the developer needs to explicitly add:

          environment:
            - THE_SECRET

This is unintuitive and could use a note in the README here with an example how that interaction works.

[jamestelfer]

I'm not a Buildkite employee, this is just my understanding as a user of the product.

The Docker plugin documents propagate-environment in its Docker repository, and notes the limitations of its use. I'd be surprised to see notes on the implementation of the Docker plugin here, particularly as any such guidance is likely to get out of date.

Or would you suggest a more general "When Docker is in use (directly or via a plugin), note that environment variables need to be forwarded to the container environment explicitly."

If this is the case, you could submit a PR to this effect?