leverage containerd image pinning

[BenTheElder]

So we can potentially re-enable image GC. #735

@ruiwen-zhao added this to containerd 1.6+ (not sure specific version yet) and we should leverage it for the pre-loaded images in kind.

[roman-kiselenko]

Hey! I want to work on this.
/cc @BenTheElder @aojea

[BenTheElder]

hey!

So I started looking into this and we'll need to label the images with --label io.cri-containerd.pinned=pinned --label io.cri-containerd.image=managed.

I know this is available for ctr images pull, we need to verify if it is for import and if not we'll need to PR that upstream first.

Also, we need to be on a sufficiently new conatinerd release first. I didn't track down exactly which version yet, that would be helpful.

We then need to decide which images this applies to.
I think to start we should do all images in kindest/node but NOT later added kind load ... images.

Turning on GC afterwards remains an open question, there's some bad trade-offs there:

1. What about user side-loaded images? Maybe we should? This could be surprising behavior.
2. image GC knobs are based on % of disk, but the host disk is not being used exclusively for this cluster and on a desktop maybe 90% full disk doesn't mean we should GC images ..... turning this on is definitely a breaking change and it's not clear what the threshold is.

Still, we can at least go ahead and clearly label kind's core bundled images as "don't GC this".

[roman-kiselenko]

we need to verify if it is for import and if not we'll need to PR that upstream first.

Yep, the labeling is only available for pull and there is no --label option for import. 😞

Status of image pinning feature:

• The feature was introduced in containerd 1.6.22 and containerd 1.7.3
• There's a follow-up fix available in containerd 1.6.25 and containerd 1.7.10

I've implemented a simple pin logic for the node-image building process here #3444

[BenTheElder]

Yep, the labeling is only available for pull and there is no --label option for import. 😞

We should work with containerd to add this feature.

[roman-kiselenko]

Yep, the labeling is only available for pull and there is no --label option for import. 😞

We should work with containerd to add this feature.

I'll give it a try and propose changes to the containerd. 🙏

[roman-kiselenko]

I've opened a PR with related changes in the containerd repo and updated the related PR in the kind repo.

[roman-kiselenko]

PR with --label flag merged.

Flag will be available in the next major release.