There are several environment variables listed in the generator base image's Dockerfile that are required when publishing using the generator base image.
The environment variables are not necessary when building the generator automation image nor when building an SDK's Dockerfile, only when running the SDK Docker image, because that is when publishing occurs.
Additionally, each SDK's templates/Dockerfile expects to be run in the context of the entire repo. This will almost always be the case, but it's worth noting that running the Dockerfile separately from the repository directory is not supported.