allow setting per connection buffer limit on Gateway with annotation

[puertomontt]

Description

#11387

Allow setting listener-level perConnectionBufferLimitBytes.

Change Type

/kind new_feature

Changelog

Allow setting listener-level perConnectionBufferLimitBytes by setting the `kgateway.dev/per-connection-buffer-limit` annotation on the gateway. 

Additional Notes

We discussed several options for setting perConnectionBufferLimitBytes.

• Creating new policy for listener options
  • decided against this since it was overkill to create a new policy for one field, and we're unlikely to have other listener level fields even in future
• adding this option to GatewayParameters
  • while this makes sense, it will require a lot of up front work to refactor it out of deployer and into krt collections

We decided using an annotation on the gateway made sense and was straightforward to implement.

[Copilot]

Pull Request Overview

This PR introduces support for a new annotation (kgateway.dev/per-connection-buffer-limit) that sets a per-connection buffer limit on Gateway listeners. Key changes include:

• Adding PerConnectionBufferLimitBytes fields to IR structs and backend Gateway representation
• Parsing the annotation into a uint32 in the KRT indexer
• Propagating the limit into Envoy listener configs via the IR translator
• Adding an end-to-end translator test for the new feature

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
pkg/pluginsdk/ir/gw2.go	Added PerConnectionBufferLimitBytes to ListenerIR and GatewayIR
pkg/pluginsdk/ir/backend.go	Added PerConnectionBufferLimitBytes to backend Gateway IR
internal/kgateway/translator/irtranslator/gateway.go	Populating listener’s PerConnectionBufferLimitBytes in Envoy config
internal/kgateway/translator/gateway_translator.go	Mapping limit on translator output
internal/kgateway/krtcollections/policy.go	Parsing annotation into uint32 and attaching to Gateway IR
api/annotations/gateway.go	Declared annotation constant
internal/kgateway/translator/gateway/gateway_translator_test.go	Added translator test case for per-connection buffer limit

Comments suppressed due to low confidence (1)

internal/kgateway/translator/gateway/gateway_translator.go:87

• The per-connection buffer limit is being applied at the gateway level here, but it should be applied per listener. Remove or relocate this field mapping and ensure it’s set individually on each listener in Translate.

		PerConnectionBufferLimitBytes: gateway.PerConnectionBufferLimitBytes, // wrong place???

[lgadban]

design doc: #11515