Add fallback logic to support multiple endpoints

[rlakhtakia]

#414

[netlify]

✅ Deploy Preview for gateway-api-inference-extension ready!

Name	Link
🔨 Latest commit	8bfdd35
🔍 Latest deploy log	https://app.netlify.com/projects/gateway-api-inference-extension/deploys/687e6a74ad3d0100086bbbd9
😎 Deploy Preview	https://deploy-preview-1122--gateway-api-inference-extension.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify project configuration.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: rlakhtakia
Once this PR has been reviewed and has the lgtm label, please assign ahg-g 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

[k8s-ci-robot]

Hi @rlakhtakia. 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.

[nirrozenbaum]

mostly already implemented in #1059

[ahg-g]

I think there is still some work to be done to actually return multiple endpoints, can we please rebase and address what is left?

[rlakhtakia]

/ok-to-test

[k8s-ci-robot]

@rlakhtakia: Cannot trigger testing until a trusted user reviews the PR and leaves an /ok-to-test message.

In response to this:

/ok-to-test

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.

[rlakhtakia]

@ahg-g @nirrozenbaum updated conflicts to remove duplicated logic from #1059

The main change incorporated now is to add the multiple endpoints to the header response.

[nirrozenbaum]

/ok-to-test

[nirrozenbaum]

This is a bit problematic.

reqCtx.TargetPod is used later to call PostResponse plugins and we should call the plugins with the pod that served the request (the first pod did not necessarily serve it, if the request failed and used fallback to next endpoint).

up until today we used a single endpoint, so that assumption was safe (either the request succeeded and then this is the pod, or it failed). but this assumption is no longer true and reqCtx.TargetPod should be updated correctly to reflect the pod that served the request.

[rlakhtakia]

I added some functionality to have multiple target pods. If we don't want to disrupt the current flow, I can add an extra field labelled 'FallbackPods' which will be the remaining list of pods

[nirrozenbaum]

last change is making changes to the scheduler interfaces.. that wasn't the intention :)
the interfaces shouldn't change (I'm referring to PostResponse interface).

in the last change the problem just moved from the director to PostResponse. in PostResponse we need to know which pod actually SERVED the request. there is only one such pod.
not the first one out of the candidate list (cause the first one didn't necessarily served the request, this is the whole point of supporting multiple endpoints).

[rlakhtakia]

/retest