Support a "from" field in targetRef for policy attachment

[LiorLieberman]

What would you like to be added: A new from field to PolicyTargetReference that will help narrowing down policy scopes based on "from" where the packet arrived.

Why this is needed: The idea of adding a from field has been brought up a few times already. The two most recent examples are the Retry Budget GEP, and BackendTLSPolicy enahcements.

It is useful in many use cases such as:

• A backendTLSPolicy thats applied to traffic thats destined to a target only if it came from HTTPRoute X, from Gateway Y, or from impl specific CustomResource
• A retry budget config thats only applicable for traffic coming from Gateway foo or from Mesh
• Supporting shared Policies across different implementations, where some implementations may not support all fields, and scoping by from enables graceful degradation or compatibility.

[youngnick]

This has come up a few times before, and I can see the uses.

But it does add yet another dimension to the "possible effective Policy" calculations. We need to be sure that the utility gained is worth the additional complexity cost we're adding to something that's already pretty complex.

[k8s-triage-robot]

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/lifecycle stale

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/lifecycle rotten

[k8s-triage-robot]

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/close not-planned

[k8s-ci-robot]

@k8s-triage-robot: Closing this issue, marking it as "Not Planned".

In response to this:

The Kubernetes project currently lacks enough active contributors to adequately respond to all issues and PRs.

This bot triages issues according to the following rules:

• After 90d of inactivity, lifecycle/stale is applied
• After 30d of inactivity since lifecycle/stale was applied, lifecycle/rotten is applied
• After 30d of inactivity since lifecycle/rotten was applied, the issue is closed

You can:

• Reopen this issue with /reopen
• Mark this issue as fresh with /remove-lifecycle rotten
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Please send feedback to sig-contributor-experience at kubernetes/community.

/close not-planned

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