auto update without registry on local images

[vrothberg]

/kind feature

Description

After a private chat with a user on auto updates, it became clear that auto updates could also be applied without having a container registry. For instance, when images built locally, the use case remains the same. Currently, auto updates only work when the image on the remote registry has changed.

There a couple of things to think about:

• Currently, containers configured for auto updates must use fully-qualified image references. Short names are not supported. Should this change? It seems very common to just use short names locally.
• Should we introduce a new auto-update policy? Currently it's called "image" (and maybe should be aliased to "registry"). The local one could be called "local". Then we could easily support short names.

@fatherlinux @mrguitar ... do you have feedback suggestions?

[mrguitar]

The majority of the "production" use cases seem to prefer separating builds from runtime environments. That said, I like this idea and it seems really useful for certain types of use cases. This would be valuable for my home systems and I can see other development-ish use cases where this would be helpful.

Agreed that short names are common for local use. I don't have a strong opinion on good options here, but would requiring "localhost/[name]" be an acceptable compromise? requiring a local policy feels cumbersome, but it's possible that's a better option.

[fatherlinux]

+1 Ben. Also, since we have the secure short names feature now (or will), I think this could probably be done in a way has defense in depth and prevents an attack from a man in the middle.

I could also see this being used in an environment with really slow internet connection. It might be cheaper to deliver a Dockerfile/Containerfile out and have the image build from some local cache of packages. It's probably an edge case, but could be really convenient if you happen to be a user with that edge case.

[github-actions]

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[rhatdan]

@vrothberg Is this is issue you wanted @ParkerVR to look at?

[ParkerVR]

@rhatdan touched based with @vrothberg on this and will discuss more in depth tmmr

[github-actions]

A friendly reminder that this issue had no activity for 30 days.

[vrothberg]

Implemented in #10063.