Merge pull request #822 from hbagdi/gep/820

GEP: introduce GEP 820

Author: k8s-ci-robot

site-src/geps/gep-820.md

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+# GEP-820: Drop extension points from Route matches
+
+* Issue: [#820](https://github.com/kubernetes-sigs/gateway-api/issues/820)
+* Status: Implementable
+
+## TLDR
+
+Drop extension points within Route match block. These extension points are
+not well understood.
+
+## Goals
+
+- Drop the extension points within Route match block.
+
+## Non-Goals
+
+- Figure out a replacement solution for the use-case that these extension
+  points addressed
+
+## Introduction
+
+As the API moves towards `v1alpha2`, the maintainers intend to make the API
+stable and forward compatible for the foreseeable future. To that end,
+maintainers intend to minimize (eliminate if possible) breaking changes post
+`v1alpha2`. This GEP is part of that initiative.
+
+Extension points for match criteria in Routes were added to enable use-cases
+where match criteria defined by implementation was a super-set of match
+criteria defined within this API. To the best of our knowledge, even though
+extension points were added, no concrete examples or use-cases were known at
+that time and none have been discovered so far.
+
+This proposal advocates removal of these extension points because:
+
+- It goes against the unwritten design principles this API has followed so far: 
+
+  - minimize number of API types as much as possible
+  - minimize strongly coupled API types and instead shoot for self-contained
+    types.
+  - extension points are introduced with clear use-cases and possibilities in
+    mind. Vague extension points are avoided as they become harder to maintain.
+- It is unlikely that the user experience resulting from defining two k8s
+  resources for defining a Route will be optimal.
+- There is not prior art on splitting match criteria and backend forwarding
+  semantics (spec.backends) in the community. We believe they are kept together
+  for good reasons.
+
+## API
+
+The following fields and all associated documentation will be removed:
+
+- HTTPRouteMatch.ExtensionRef
+- TCPRouteMatch.ExtensionRef will be removed. This results in a struct without
+  any members: TCPRouteMatch. The struct will be kept as it is expected that
+  more match criterias might be added to L4 routes.
+
+  - Do the same to UDPRoute and TLSRoute
+
+## Alternatives
+
+N/A
+