Add support for custom vm extensions

[willie-yao]

What type of PR is this?
/kind feature

What this PR does / why we need it:
This PR adds support for deployment of custom VM extensions from the Azure Extension gallery as part of a VM and VMSS deployment.

Which issue(s) this PR fixes:
Fixes #2221

Special notes for your reviewer:
In order to test the extension provisions successfully, I used Tilt to deploy the default flavor. I added the VMExtensions field to the default cluster template's AzureMachineTemplate spec like so:

vmExtensions:
      - name: CustomScript
        publisher: Microsoft.Azure.Extensions
        version: '2.1'
        settings:
          skipDos2Unix: false
        protectedSettings:
          commandToExecute: |
            #!/bin/sh
            echo "Updating packages ..."
            apt update
            apt upgrade -y

Please confirm that if this PR changes any image versions, then that's the sole change this PR makes.

TODOs:

• squashed commits
• includes documentation
• adds unit tests

Release note:

Add support for custom vm extensions

[k8s-ci-robot]

Hi @willie-yao. Thanks for your PR.

I'm waiting for a kubernetes-sigs 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.

I understand the commands that are listed here.

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.

[mboersma]

/ok-to-test

[willie-yao]

/retest

[willie-yao]

/retest

[willie-yao]

/retest

[CecileRobertMichon]

/lgtm
/assign @Jont828 @jackfrancis

[CecileRobertMichon]

Thanks for adding this doc, looks good 💯

Can you please add it to https://github.com/kubernetes-sigs/cluster-api-provider-azure/blob/7d8dc8583b1c8db99a84768e5ed7f2f140983a05/docs/book/src/SUMMARY.md?plain=1 under Topics so it shows up in the book Table Of Content?

[willie-yao]

Got it! I'll add it under the other "custom" topics. I'm not sure if there is a specific ordering of topics, but I felt like that would be the best place to add it!

[CecileRobertMichon]

Topics are ordered alphabetically I think (except the first two)

[willie-yao]

I thought so too, but it seems like a few are out of order. "Custom Images" is under "Custom Private DNS Zone name", and there are a few others like "SSH Access to nodes". Should we standardize how we order the topics?

[CecileRobertMichon]

I'm guessing "Custom Private DNS Zone" is ordered by file name "custom-dns" (d comes before i) and "SSH Access to nodes" was likely just added at the end by someone who didn't realize the list was in order. Feel free to reorganize/rename however you see fit, the ordered list is becoming less practical now that we have so many topics, maybe we need sub-sections now. This can be a separate PR so it doesn't block this one.

[CecileRobertMichon]

/lgtm

[willie-yao]

@CecileRobertMichon I saw that there is a failed test with broken links. I'm assuming this is intended because the link for the new docs page hasn't been published yet. Is that correct?

[jackfrancis]

@CecileRobertMichon I saw that there is a failed test with broken links. I'm assuming this is intended because the link for the new docs page hasn't been published yet. Is that correct?

It's just bad luck, I got the same error on my PR, here's the fix:

https://github.com/kubernetes-sigs/cluster-api-provider-azure/pull/2680/files#diff-4d554fade8fefc047dcf883418cc72311cb5b62f3e0d20f7cbbfb849faa7335aR525

tl;dr k8s maintains 4 versions of that link, and then garbage collects the oldest one when a new release is needed

Not sure if we wanna include it in this PR or rebase this on top of a PR that fixes it :(

[willie-yao]

@jackfrancis Oh that makes sense! If this blocks merging, I'm not sure what's the better way to do it. I'm leaning towards including this in a separate PR since it's not related to custom vm extensions.

[jackfrancis]

@willie-yao you can rebase on top of latest main as this PR delivered the needful: #2680

[willie-yao]

@jackfrancis @CecileRobertMichon Did the rebase and the test passes now. Does everything look good for approval?

[jackfrancis]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jackfrancis

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [jackfrancis]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment