Add support for the images={} attribute.

[mattmoor]

When the images={} attribute is specified resolution will publish the collection of images, and substitute the exact digest of the published image as part of resolution (avoids race condition).

[mattmoor]

@dlorenc It is notable that this won't work with minikube unless the user's roundtripping through a real registry.

(thinking out loud)
That said, we can probably put together an alternate implementation of Publish() that supports docker loading the image into minikube's docker daemon. If we put this in a little library in rules_docker then we could also use it to implement this, which is a nice two-for-one.

WDYT?

[dlorenc]

Is index used anywhere?

[mattmoor]

Yeah, where I increment it :) Removed.

[rohansingh]

That said, we can probably put together an alternate implementation of Publish() that supports docker loading the image into minikube's docker daemon.

@mattmoor I've put together some rules and a macro for a repo that basically does this. Notes for anyone that wants to take a stab on a real implementation:

1. The difficult part was deciding how to tag the images locally, since locally-loaded Docker images can't be referenced by digest. I ended up just tagging the images with their digest value.

2. I didn't want to tackle rewriting the incremental loader from rules_docker in Python. Instead, I just created a separate rule that wraps incremental_load from @io_bazel_rules_docker//container:layer_tools.bzl to load the image, and then wraps k8s_object to do Kube stuff.

3. Because of the above, I didn't change Publish() to load the image into the Docker daemon. Instead, the resolver just accepts a --no_upload flag. When passed, it does not upload the image. Instead, it resolves the image name using the tag strategy described above.

Obviously this is a bit of a hacky solution, but it seems to work quite reliably. Having the ability to deploy manifests locally like this is really handy.

[mattmoor]

FWIW I solved this in ko by simply tagging the image with the digest, see: https://github.com/google/go-containerregistry/blob/master/cmd/ko/README.md

[mattmoor]

Note: my bias towards not using :latest was that it doesn't work well with K8s default pull policy.