docs: add IngressClassParams KEP

keps/0009-ingress-class-params-crd.md

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+---
+title: Introduce IngressClassParameters CRD to control IngressClass behavior
+status: provisional
+---
+
+# Introduce IngressClassParameters CRD to control IngressClass behavior
+
+<!-- toc -->
+- [Summary](#summary)
+- [Motivation](#motivation)
+ - [Goals](#goals)
+- [Proposal](#proposal)
+ - [Graduation Criteria](#graduation-criteria)
+- [Implementation History](#implementation-history)
+<!-- /toc -->
+
+## Summary
+
+Currently users can control how traffic is load-balanced for an `Ingress`
+resource using the [`ingress.kubernetes.io/service-upstream` annotation][service-upstream-annotation].
+This can quickly get cumbersome, specifically for environments with large number
+of `Ingress` resources.
+
+Controlling `IngressClass` parameters in one place would be much more desirable in
+such situations, hence the proposal to introduce a new object - `IngressClassParameters` -
+which would allow said customizations.
+
+[service-upstream-annotation]: https://docs.konghq.com/kubernetes-ingress-controller/2.3.x/references/annotations/#ingresskubernetesioservice-upstream
+
+## Motivation
+
+- we want to allow `IngressClass` behavior customizations in one place
+- we want to make configuration management related to `IngressClass` to not be
+ a burden for the user even when IngressClass is assigned to many services
+
+### Goals
+
+- provide a definition of new object - `IngressClassParameters`
+- provide an _ability to configure_ `IngressClass` in one place via aforementioned
+ `IngressClassParameters` object
+- provide `ServiceUpstream` field in `IngressClassParameters` object, as means to control
+ the behavior already provided by `ingress.kubernetes.io/service-upstream` annotation
+
+## Proposal
+
+### Graduation Criteria
+
+- [ ] introduce `IngressClassParameters` object available for deployment for end users
+- [ ] introduce a [feature gate][feature-gates] for the functionality described in this KEP
+- [ ] `ServiceUpstream` field implemented in `IngressClassParameters` object to allow
+ control of behavior of all services handled by an `Ingress` configured with an
+ `IngressClass` that references said parameters object
+
+## Implementation History
+
+- First issue proposing to enable `service-upstream` for an entire ingress class
+ in [#774][774]
+- [#1131][1131] was raised to discuss `IngressClass` parameters more generically
+- An initial proposal has been made in [#1586][1586] (trying to address [#1131][1131])
+ but the work did not conclude and eventually the PR didn't get merged
+- Another proposal has been made in [#2535][2535] basing its work on [#1586][1586]
+
+[774]: https:/Kong/kubernetes-ingress-controller/pull/774
+[1131]: https:/Kong/kubernetes-ingress-controller/pull/1131
+[1586]: https:/Kong/kubernetes-ingress-controller/pull/1586
+[2535]: https:/Kong/kubernetes-ingress-controller/pull/2535
+[feature-gates]: ../FEATURE_GATES.md