How to mark/reject resources using unsupported features

[mlavacca]

Problem statement:

At the moment there is no standardized way to check a HTTPRoute uses an unsupported feature. At Kong, we have a validating webhook that rejects HTTPRoutes using unsupported features. GEP-2162 introduced the supportedFeatures field to highlight the features supported by the implementation, and in the future work section such topic is mentioned. A standardized and shared way of accepting or rejecting resources using unsupported features is desirable, and this issue is about sensing the community's feelings.

Proposed solution

I think a viable (and desirable) solution would be to move this logic away from implementations' webhooks and instead rely on the resources' status. We could introduce a new reason for gateways and routes Accepted condition so that no resource using an unsupported feature is accepted and proper feedback is given to the user.

[pleshakov]

Could

gateway-api/apis/v1/shared_types.go

Line 344 in a919f8b

RouteReasonUnsupportedValue RouteConditionReason = "UnsupportedValue"

work?

We use it in our implementation for HTTPRoute fields that are not supported (ex. an unsupported filter). Although, we also use it for invalid values too

[mlavacca]

Could

gateway-api/apis/v1/shared_types.go

Line 344 in a919f8b

RouteReasonUnsupportedValue RouteConditionReason = "UnsupportedValue"

work?
We use it in our implementation for HTTPRoute fields that are not supported (ex. an unsupported filter). Although, we also use it for invalid values too

They are intended for a different use, when a field value does not belong to the enum. Example:

gateway-api/apis/v1/httproute_types.go

Lines 318 to 338 in 6b8c237

	// PathMatchType specifies the semantics of how HTTP paths should be compared.
	// Valid PathMatchType values, along with their support levels, are:
	//
	// * "Exact" - Core
	// * "PathPrefix" - Core
	// * "RegularExpression" - Implementation Specific
	//
	// PathPrefix and Exact paths must be syntactically valid:
	//
	// - Must begin with the `/` character
	// - Must not contain consecutive `/` characters (e.g. `/foo///`, `//`).
	//
	// Note that values may be added to this enum, implementations
	// must ensure that unknown values will not cause a crash.
	//
	// Unknown values here must result in the implementation setting the
	// Accepted Condition for the Route to `status: False`, with a
	// Reason of `UnsupportedValue`.
	//
	// +kubebuilder:validation:Enum=Exact;PathPrefix;RegularExpression
	type PathMatchType string

[mlavacca]

@shaneutt @robscott @youngnick any thoughts on this one? Is this something we could consider to implement?

[shaneutt]

The proposal to standardize on rejecting routes based on the supportedFeatures in GatewayClass, and providing some new relevant conditions/reasons to explain when things wont work sounds good to me 👍

[youngnick]

Yes, I agree having standard conditions or reasons to explain that something is rejected because it uses an unsupported feature seems like a good idea to me as well.

[mlavacca]

Sounds good, I'll open a PR to update GEP-2162 accordingly.

[pmalek]

For those looking for GEP-2162: it has been moved to https://github.com/kubernetes-sigs/gateway-api/blob/main/geps/gep-2162/index.md