Check for existing tag in remote repo before building. (#764)

webapps are meant to be build-once/deploy-many, but we were rebuilding them for every request.  This changes that, so that we rebuild only for every unique ApplicationRecord.

When we push the image, we now tag it according to its ApplicationRecord.

We don't want to use that tag directly in the compose file for the deployment, however, as the deployment needs to be able to adjust to new builds w/o re-writing the file all the time.  Instead, we use a per-deployment unique tag (same as before), we just update what image it references as needed.

Reviewed-on: cerc-io/stack-orchestrator#764

stack_orchestrator/deploy/images.py

@@ -29,6 +29,29 @@ def _image_needs_pushed(image: str):
     return image.endswith(":local")
 
 
+def remote_image_exists(remote_repo_url: str, local_tag: str):
+    docker = DockerClient()
+    try:
+        remote_tag = remote_tag_for_image(local_tag, remote_repo_url)
+        result = docker.manifest.inspect(remote_tag)
+        return True if result else False
+    except Exception:  # noqa: E722
+        return False
+
+
+def add_tags_to_image(remote_repo_url: str, local_tag: str, *additional_tags):
+    if not additional_tags:
+        return
+
+    if not remote_image_exists(remote_repo_url, local_tag):
+        raise Exception(f"{local_tag} does not exist in {remote_repo_url}")
+
+    docker = DockerClient()
+    remote_tag = remote_tag_for_image(local_tag, remote_repo_url)
+    new_remote_tags = [remote_tag_for_image(tag, remote_repo_url) for tag in additional_tags]
+    docker.buildx.imagetools.create(sources=[remote_tag], tags=new_remote_tags)
+
+
 def remote_tag_for_image(image: str, remote_repo_url: str):
     # Turns image tags of the form: foo/bar:local into remote.repo/org/bar:deploy
     major_parts = image.split("/", 2)