Enables using scripts to modify VMI definition

[dharmit]

What this PR does / why we need it:
Presently, users need to write a Go program if they want to use the hook sidecar functionality to modify VMI's XML definition before its creation. This PR aims to let the users write a shell/python script for the same.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

Special notes for your reviewer:

Checklist

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• Design: A design document was considered and is present (link) or not required
• PR: The PR description is expressive enough and will help future contributors
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• Upgrade: Impact of this change on upgrade flows was considered and addressed if required
• Testing: New code requires new unit tests. New features and bug fixes require at least on e2e test
• Documentation: A user-guide update was considered and is present (link) or not required. You want a user-guide update if it's a user facing feature / API change.
• Community: Announcement to kubevirt-dev was considered

Release note:

Ability to run scripts through hook sidecar

[kubevirt-bot]

Hi @dharmit. Thanks for your PR.

I'm waiting for a kubevirt member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[tiraboschi]

/ok-to-test

[dharmit]

@victortoso since you have worked extensively on sidecar, can you please provide your feedback on this PR? Perhaps the README.md at cmd/example-hook-generic/README.md would help understand what I'm trying to do here.

[victortoso]

Hi @dharmit, I'll be happy to but I can't Today. Tomorrow or the day after at latest ;)
/assign

[dharmit]

The job "pull-kubevirt-generate" fails with following log:

./hack/verify-generate.sh
ERROR: git tree state is not clean!
You probably need to run 'make generate' or 'make' and commit the changes
On branch main
Changes not staged for commit:
  (use "git add/rm <file>..." to update what will be committed)
  (use "git restore <file>..." to discard changes in working directory)
	deleted:    examples/vmi-with-generic-hook.yaml
no changes added to commit (use "git add" and/or "git commit -a") 

But we need the examples/vmi-with-generic-hook.yaml file. If I delete it, I think, the tests will pass, but I need it to show a working example of what's done in this PR.

How do I ensure it's not a problem for make generate?

EDIT: Fixed this in 89e2c20.

[victortoso]

Hi, I just started looking at this, sorry the delay.

Presently, users need to write a Go program if they want to use the hook sidecar functionality to modify VMI's XML definition before its creation. This PR aims to let the users write a shell/python script for the same.

Have you tried the sidecar-shim image. The sidecar-shim binary looks for an executable in $PATH for the Hook you want to implement (e.g: onDefineDomain), check the README. I honestly haven't tested a shell/python script but I think it can be done.

I'll keep looking into the patch series to follow the ConfigMap introduction/usage

[victortoso]

I like the idea. I consider myself new to kubevirt/k8s design so it would be great to have second opinion on using ConfigMap to store scripts and creating the volumes, etc.

I'd test with sidecar-shim container image and if possible use it here. There are a few reasons for this suggestion:

1. Reduce boilerplate with gRPC
2. We can add new APIs in the hooks, implement it on the sidecar-shim and should benefit this or other sidecars that use sidecar-shim. For example, this attempt to fix second migration on VMI with sidecar.
3. It already does similar logic, like executing command on $PATH. The difference is that the command has to be the hook name.

[victortoso]

This is a very interesting approach. It means that with a single container-image we could deploy different scripts.

[victortoso]

I'd suggest moving it under the cmd/sidecars folder. I'm on the process of doing that, just waiting it to be unhold, see: #10320

[alicefr]

/lgtm

[alicefr]

/lgtm

[kubevirt-bot]

@dharmit: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-kubevirt-verify-rpms	8acea18	link	false	/test pull-kubevirt-verify-rpms
pull-kubevirt-e2e-k8s-1.26-sig-compute	cb461a2	link	unknown	/test pull-kubevirt-e2e-k8s-1.26-sig-compute
pull-kubevirt-e2e-k8s-1.27-sig-compute	cb461a2	link	unknown	/test pull-kubevirt-e2e-k8s-1.27-sig-compute

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository. I understand the commands that are listed here.