enable istio as a provider + configuring destinationRule

[Gregory-Pereira]

cc @liu-cong

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[Gregory-Pereira]

cc @SergeyKanzhelev @ahg-g

[kfswain]

Meta-question here; does a destination rule have to be provided at the time of inferencePool creation? I don't fully understand the usecase here, and so, to me, it looks like we are just extracting all the DestinationRule fields into the helm chart. That may set a pattern we don't want, where the helm chart is essentially just a wrapper over the direct K8s manifest.

Said another way; what are we simplifying by exposing the entire CRD in the helm chart?

[Gregory-Pereira]

Meta-question here; does a destination rule have to be provided at the time of inferencePool creation?

The key reason why I wanted this change, is because to properly route traffic with Istio we need a DestinationRule. The .host value for that DestinationRule needs to be the EPP service address, and so the DestinationRule is dependent on the name of the EPP service and thus the release name used when installing the GIE charts.

What we do currently (which is definitely not ideal) is create the destination rule in the infra charts, (mapping gateway traffic to a service address that does not exist yet). Then we create the release of the model-service the GIE charts which will create the other pieces of the stack, and we apply a bogus label to the HTTPRoute and or Gateway to force reconciliation.

Said another way; what are we simplifying by exposing the entire CRD in the helm chart?

In my eyes we are simplifying the user experience. AFAICT, this chart does not support extraDeploy or any method to apply or track miscellaneous but related manifests. The alternatives I see here are creating an individual DestinationRule out of band after chart application, which relies on scripting rather than coordinating helmfile releases, or guessing the service address ahead of time in infra and applying it there.

Definitely open to alternatives if you had anything better in mind.

[pierDipi]

Do we have to use Istio specific APIs (DestinationRule) or standard GW APIs can be used instead?
(for example: BackendTrafficPolicy and BackendTLSPolicy
https://gateway-api.sigs.k8s.io/api-types/backendtrafficpolicy/
https://gateway-api.sigs.k8s.io/api-types/backendtlspolicy/?h=backendtlspolicy)

[Gregory-Pereira]

Definitely open to it if you want to contribute an alternative, this is just beyond the scope of this initial implementation for integration with llm-d

[liu-cong]

Great discussions between @Gregory-Pereira and @kfswain .

The part that it creates a DestinationRule pointing to the EPP service makes sense to me (unless there are better ways to do it), similar to how we create the GCPBackendPolicy and HealthCheckPolicy for gke. To me these are necessary resources to make things work, while they are not "mandatory" info that users need to know unless they want to customize.

But if that's our goal (hide unnecessary complexity for most initial use cases), then we should probably provide a [optional] default config that works out of the box, instead of asking the user to provide the entire DestinationRule config. The current gke example provides default config that works out of the box. Then the question becomes what's the minimal DestinationRule config required to get things to work? Is it just the host part?

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[liu-cong]

/lgtm

From what I can tell from our Istio doc, this is needed for Istio routing to work. I tink this is a nice to have, and we can simplify the Istio installation doc once this is in.

[k8s-ci-robot]

New changes are detected. LGTM label has been removed.

[danehans]

This PR needs a link to an issue or a more detailed description of what the problem is and how this PR fixes it.

/hold

[danehans]

xref: #1475 that refactors the setup guide and may affect this PR.

[k8s-ci-robot]

PR needs rebase.

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