add additional-images flag to build command

[dkoshkin]

A solution for #2063

Add a way to specify additional images to pull when running kind build node-image with a new flag --additional-images.

My use-case is to have a kind image that is used in an air-gapped cluster that includes a few additional images.
There is no easy way to extend the existing kindest/node images (please correct me here if there is some process), kind load is an option but its less desirable for my use case since it would require to package and ship around multiple images instead of just the one kindest/node image.

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[BenTheElder]

Please file a feature request and discuss a design first: https://kind.sigs.k8s.io/docs/contributing/getting-started/#4-reaching-out
(we are looking at instituting a better process for recording proposals, but in the meantime we use feature issues)

Some questions to consider:

• should we pull images if they're not present locally?
  • if we're pulling images, should we just pull them directly to containerd instead of to the host?
• what about podman?
• what about tarballs / image archives?
• what about image eviction in the future? should kind be responsible for somehow preventing these images from being evicted if we re-enable eviction once we have a solution for the core images?
• could we instead support this in a way that involved extending an existing node image without having to build from source? would that be better?

EDIT: We are also looking to stabilize the CLI, APIs, etc., so we want to consider future usage etc. before adding features, so we can avoid needing to make a breaking change to it to support the full set of use cases.
EDIT2: Thanks for the PR as well though 😅

[dkoshkin]

Hi @BenTheElder thanks for the quick reply!

Sorry should have dug around the docs more to find the contributing process, as you may have guessed this is my first attempt at a contribution to kind 😰

I created a feature ticket #2160 so I can close this and move the discussion there?

[k8s-ci-robot]

@dkoshkin: The following tests failed, say /retest to rerun all failed tests:

Test name	Commit	Details	Rerun command
pull-kind-e2e-kubernetes-1-19	6162253	link	/test pull-kind-e2e-kubernetes-1-19
pull-kind-e2e-kubernetes-1-20	6162253	link	/test pull-kind-e2e-kubernetes-1-20
pull-kind-e2e-kubernetes	6162253	link	/test pull-kind-e2e-kubernetes

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[BenTheElder]

No worries! We need to put more effort into surfacing this and improving the process 😅

Apologies in advance for the scattered response latency, we're trying to wrap up some things for the next release and all of us work on other projects as well (upstream kubernetes in particular). I know Antonio and I also have a little bit of time out / vacation intermittently in the next two weeks.

[k8s-ci-robot]

@dkoshkin: PR needs rebase.

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[BenTheElder]

I think #2303 will be a more powerful alternative based on the discussion in the #2160. (and save people the trouble of having to build a node image again)

[BenTheElder]

thanks again for the PR! tentatively closing in favor of the other approach