ResolvedRefs=False/EndpointsNotFound on HTTPRoute with RequestMirror filter when backend scaled to 0

[kajanan1212]

Observation

When a deployment using an HTTPRoute with a RequestMirror filter is scaled to 0 replicas, we observe the following conditions on the route:

{                                                                                                                                                               
    "reason": "EndpointsNotFound",
    "status": "False", 
    "type": "ResolvedRefs"
},                                                                                                                                                              
{                          
    "reason": "EndpointsNotFound",
    "status": "False",
    "type": "BackendsAvailable"
}

For a primary BackendRef backend scaled to 0, we only see BackendsAvailable=False/EndpointsNotFound, ResolvedRefs stays True. But for the RequestMirror backend, ResolvedRefs is also set to False.

Question

Is ResolvedRefs=False/EndpointsNotFound the intended behaviour for RequestMirror filter backends?

We ask because we noticed this comment in route.go for the primary backend path:

// Gateway API conformance: When backendRef Service exists but has no endpoints,                                                                                
// the ResolvedRefs condition should NOT be set to False.
if err.Reason() == status.RouteReasonEndpointsNotFound {                                                                                                        
    errorCollector.Add(err.WithType(status.RouteConditionBackendsAvailable))
}

This aligns with our understanding, the service exists and is correctly referenced, so ResolvedRefs should remain True.

The distinction between "reference resolution" and "backend availability" was also the motivation behind PR #6315, where the author (@kkk777-7) noted:

"the Gateway API Conformance test fails when ResolvedRefs is set to false in the absence of an endpoint"

Should the same treatment apply to RequestMirror backends, or is there a reason the behaviour differs?

Environment

• Envoy Gateway: v1.6+ (After feat: add validation of backend endpointslice #6315)

[arkodg]

cc @kkk777-7

[kkk777-7]

Hi @kajanan1212 , thanks for raising this discussion!
I think RequestMirror should be treated same behaivor as primary. so, I'll create Issue and work on fix.

[kkk777-7]

Hi @kajanan1212
we merged #8675, so it will be fixed once version (v1.8.0-rc.1, v1.7.2, v1.6.6) is released.

[kajanan1212]

@kkk777-7, thanks for the quick turnaround on this !

Really appreciate you confirming it as a bug and getting the fix merged so fast.

Looking forward to the upcoming releases with the fix included.