feat: adding support for creating targets from ExternalName

[msvticket]

Issue

#3505

Description

I added support for ip target groups when service is of type ExternalName.

I have not updated any documentation, but I'm happy to do that in case you want the code change to begin with.

Checklist

• Added tests that cover your change (if possible)
• Added/modified documentation as required (such as the README.md, or the docs directory)
• Manually tested
• Made sure the title of the PR is a good description that can go into the release notes

BONUS POINTS checklist: complete for good vibes and maybe prizes?! 🤯

• Backfilled missing tests for code in same general area 🎉
• Refactored something and made the world a better place 🌟

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[msvticket]

Could you have a look at this @oliviassss ?

[Leen15]

any update on this?

[MateuszWkDev]

I woul like to get update on this as this seems much needed functionality in order to support certain usecases

[Reyalsorik]

Any update? I would appreciate this functionality.

[nousot-cloud-guy]

Is there anything that's holding up this PR that someone could help finish? This would be really useful functionality to have.

[msvticket]

Is this something you can look at @shraddhabang?

[felipegouveiae]

@johngmyers @M00nF1sh please review and merge! I'm begging you!

[msvticket]

Hi @zac-nixon!

You seem to be a newish active maintainer of aws-load-balancer-controller. Can you please review this old PR? I've just rebased it on main, built it and tested it on a staging cluster.

[deens-cyera]

Hey, any update in the pr ?

[chris-codaio]

Another vote to get this reviewed & committed - just ran into this limitation this week!

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: msvticket
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[zac-nixon]

Hi. I'd like to update everyone on the conversation we had in Slack.

Zac Nixon
  [1:55 PM](https://kubernetes.slack.com/archives/D09ARVB64TF/p1755723355218379)
I reviewed the PR, the code your wrote makes sense but I have a concern. How does the controller know that the DNS record has been updated, so that it can update the target group? Right now, you're relying the sync time (~10 hours) to do the DNS updates. It seems that we would need some background process that is querying dns periodically and enqueuing events when the record changes.


Mårten Svantesson
  [8:51 AM](https://kubernetes.slack.com/archives/D09ARVB64TF/p1755791499599059)
Well, my thought is that this is an initial implementation that I tried to keep as simple as possible. You are right in that it probably wont suffice for everybody, but I think it is better to base improvements on feedback rather than guesses.


Zac Nixon
  [7:53 AM](https://kubernetes.slack.com/archives/D09ARVB64TF/p1755874427108159)
Yeah, I see what you're saying. I really appreciate the PR, but generally we don't accept features that aren't complete. Not having a way to timely update the LoadBalancer when the DNS entries changes seems like a big problem. Can you explain how this feature helps you out?


Mårten Svantesson
  [7:09 AM](https://kubernetes.slack.com/archives/D09ARVB64TF/p1756130961627789)
I use it to implement this solution: https://aws.amazon.com/blogs/networking-and-content-delivery/hosting-internal-https-static-websites-with-alb-s3-and-privatelink/
By using an ExternalName for s3 I don’t need a separate ALB but can use the same that is used for accessing internal application running in EKS.
Amazon Web ServicesAmazon Web Services
[Hosting Internal HTTPS Static Websites with ALB, S3, and PrivateLink | Amazon Web Services](https://aws.amazon.com/blogs/networking-and-content-delivery/hosting-internal-https-static-websites-with-alb-s3-and-privatelink/)
Amazon Simple Storage Service (Amazon S3) is a powerful platform that enables you to do various tasks. One notable feature is the ability to create a bucket with an FQDN, point an alias record to the bucket website endpoint, and immediately get up-and-running with an HTTP static website. If you want to serve HTTPS traffic […]
Dec 30th, 2022
https://aws.amazon.com/blogs/networking-and-content-delivery/hosting-internal-https-static-websites-with-alb-s3-and-privatelink/



Zac Nixon
  [8:36 AM](https://kubernetes.slack.com/archives/D09ARVB64TF/p1756136188696239)
Thanks for the link. I suspect that this works for your case because AFAIK, Private Link uses a static IP address.
[8:37](https://kubernetes.slack.com/archives/D09ARVB64TF/p1756136238044719)
Generally, we would like to supply more general solutions, this one has a pretty sharp edge where Target Group changes aren't propagated very fast.

TL;DR - There is some more work to be done here to accept this change. I don't really have the time until ~October to put more stuff on my plate.

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[msvticket]

/remove-lifecycle stale