feat(source): add gateway api hostname source annotation

[hjoshi123]

What does it do ?

Adds external-dns.alpha.kubernetes.io/gateway-hostname-source annotation to the GatewayAPI source.

Motivation

#5391

More

• Yes, this PR title follows Conventional Commits
• Yes, I added unit tests
• Yes, I updated end user documentation accordingly

[k8s-ci-robot]

Hi @hjoshi123. 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-sigs/prow repository.

[ivankatliarchuk]

/ok-to-test

[mloiseleur]

At first glance, it makes sense.
@abursavich Wdyt ? Anything I missed ? Do you think you can review this PR ?

[bdrewery]

I ran into a case of needing this too.
Probably should update docs/annotations/annotations.md or docs/sources/gateway-api.md or any doc.

[ivankatliarchuk]

Hi @bdrewery,

Would you be able to share an abstract with a use case for that annotation? This would be incredibly helpful for our documentation; it's always valuable to provide not just the feature itself, but also practical examples of how it can be used.

[ivankatliarchuk]

I think there is a great explanation about one of the use cases, we could re-use and add it to docs #5391 (comment)

Customers need to be able to resolve most of their traffic over the private endpoint, so they set up DNS for company.private.example.com to point to their internal VPC endpoint. The CNAME then directs traffic from company.public.example.com to company.private.example.com which resolves privately to their internal endpoint. This is then directed to our Gateway API private load balancer, then routed in-cluster.

Some limited traffic from third-party services that our customers use (namely SCIM) cannot traverse this private endpoint, so we need to have that traffic be able to resolve company.private.example.com to our public gateway instead. Inside their network, that will still resolve to their internal endpoint, but those third-party services will be able to send traffic to the public endpoint (which will only handle traffic for a \scim endpoint and blackhole everything else).

The problem is that the hostname those third-party services will have to use is company.public.example.com, so that's the hostname that we need to use on our HTTPRoute. We don't want to override our CNAME however, or that will break our customers other operations. We want external DNS to create ONLY an A record for company.private.example.com -> public gateway loadbalancer DNS, but the default behavior is to add both the hostname annotations and the hostname defined in the HTTPRoute spec, which causes it to override our ExernalName service's CNAME record with a message like this:

[hjoshi123]

@ivankatliarchuk yes I was gonna modify the documentation for ingress since the annotation's purpose is similar

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
Once this PR has been reviewed and has the lgtm label, please assign ivankatliarchuk for approval. For more information see the Code Review Process.

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

Needs approval from an approver in each of these files:

• OWNERS

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

[hjoshi123]

@bdrewery @ivankatliarchuk added documentation.. let me know if the documentation works

[ivankatliarchuk]

/ok-to-test

[ivankatliarchuk]

In docs use-cases missing. And would you be able to share evidences that the code is working and make changes expected?

[hjoshi123]

Hmm.. @ivankatliarchuk I will try running it on my homelab over the weekend.. if someone can do it earlier then it would be better too.. the unit tests are passing though
also I think I did add the use-cases in docs/sources under why is this needed?

[mloiseleur]

/ok-to-test

[ivankatliarchuk]

Example use cases for another annotation https://github.com/kubernetes-sigs/external-dns/blob/master/docs/advanced/ttl.md#use-cases-for-external-dnsalphakubernetesiottl-annotation. This will help us and a community to decide which annotation to use

[hjoshi123]

Ah gotcha @ivankatliarchuk I can add it.. although I didn't get time to run this on a cluster.. but seems like the tests are passing.. I am not sure if any of you guys have bandwidth to try it out

[k8s-ci-robot]

PR needs rebase.

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-sigs/prow repository.

[KalenWessel]

Checking in to see when this functionality will be merged in? I'm currently running into a similar scenario outlined in this comment

[ivankatliarchuk]

This PR abandoned. If anyone interested to add feature what is required;

• feat(source): add gateway api hostname source annotation #5487 (comment)
  So just run it against a cluster and confirm it's working.

Example result #5828 (comment)

If needed, see how to test a PR. This will require golang to be installed.