gatewayapi: add support for b/g mirroring

Add support for mirroring requests while performing B/G deployments with
Gateway API. A `RequestMirror` filter pointing to the canary service is
added to the HTTPRoute during a Canary run. During the Canary run, drift
correction for `.spec.rules[].filters` is disabled to avoid removing the
mirror filter.

Signed-off-by: Sanskar Jaiswal <jaiswalsanskar078@gmail.com>

pkg/router/gateway_api_v1beta1.go

@@ -187,6 +187,16 @@ func (gwr *GatewayAPIV1Beta1Router) Reconcile(canary *flaggerv1.Canary) error {
 		ignoreCmpOptions = append(ignoreCmpOptions, cmpopts.IgnoreFields(v1beta1.HTTPBackendRef{}, "Filters"))
 	}
 
+	if canary.GetAnalysis().Mirror {
+		// If a Canary run is in progress, the HTTPRoute rule will have an extra filter of type RequestMirror
+		// which needs to be ignored so that the requests are mirrored to the canary deployment.
+		inProgress := canary.Status.Phase == flaggerv1.CanaryPhaseWaiting || canary.Status.Phase == flaggerv1.CanaryPhaseProgressing ||
+			canary.Status.Phase == flaggerv1.CanaryPhaseWaitingPromotion
+		if inProgress {
+			ignoreCmpOptions = append(ignoreCmpOptions, cmpopts.IgnoreFields(v1beta1.HTTPRouteRule{}, "Filters"))
+		}
+	}
+
 	if httpRoute != nil {
 		specDiff := cmp.Diff(
 			httpRoute.Spec, httpRouteSpec,
@@ -249,6 +259,12 @@ func (gwr *GatewayAPIV1Beta1Router) GetRoutes(canary *flaggerv1.Canary) (
 				}
 			}
 		}
+		for _, filter := range rule.Filters {
+			if filter.Type == v1beta1.HTTPRouteFilterRequestMirror && filter.RequestMirror != nil &&
+				string(filter.RequestMirror.BackendRef.Name) == canarySvcName {
+				mirrored = true
+			}
+		}
 	}
 
 	if weightedRule != nil {
@@ -307,6 +323,23 @@ func (gwr *GatewayAPIV1Beta1Router) SetRoutes(
 			},
 		},
 	}
+
+	// If B/G mirroring is enabled, then add a route filter which mirrors the traffic
+	// to the canary service.
+	if mirrored && canary.GetAnalysis().Iterations > 0 {
+		weightedRouteRule.Filters = append(weightedRouteRule.Filters, v1beta1.HTTPRouteFilter{
+			Type: v1beta1.HTTPRouteFilterRequestMirror,
+			RequestMirror: &v1beta1.HTTPRequestMirrorFilter{
+				BackendRef: v1beta1.BackendObjectReference{
+					Group: (*v1beta1.Group)(&backendRefGroup),
+					Kind:  (*v1beta1.Kind)(&backendRefKind),
+					Name:  v1beta1.ObjectName(canarySvcName),
+					Port:  (*v1beta1.PortNumber)(&canary.Spec.Service.Port),
+				},
+			},
+		})
+	}
+
 	httpRouteSpec := v1beta1.HTTPRouteSpec{
 		CommonRouteSpec: v1beta1.CommonRouteSpec{
 			ParentRefs: canary.Spec.Service.GatewayRefs,

pkg/router/gateway_api_v1beta1_test.go

@@ -233,6 +233,44 @@ func TestGatewayAPIV1Beta1Router_Routes(t *testing.T) {
 		}
 		assert.True(t, found)
 	})
+
+	t.Run("b/g mirror", func(t *testing.T) {
+		canary := mocks.canary.DeepCopy()
+		canary.Spec.Analysis.Mirror = true
+		canary.Spec.Analysis.Iterations = 5
+		_, _, cSvcName := canary.GetServiceNames()
+
+		err = router.SetRoutes(canary, 100, 0, true)
+		hr, err := mocks.meshClient.GatewayapiV1beta1().HTTPRoutes("default").Get(context.TODO(), "podinfo", metav1.GetOptions{})
+		require.NoError(t, err)
+		assert.Len(t, hr.Spec.Rules, 1)
+
+		rule := hr.Spec.Rules[0]
+		var found bool
+		for _, filter := range rule.Filters {
+			if filter.Type == v1beta1.HTTPRouteFilterRequestMirror && filter.RequestMirror != nil &&
+				string(filter.RequestMirror.BackendRef.Name) == cSvcName {
+				found = true
+			}
+		}
+		assert.True(t, found, "could not find request mirror filter in HTTPRoute")
+
+		// Mark the status as progressing to assert that request mirror filter is ignored.
+		canary.Status.Phase = flaggerv1.CanaryPhaseProgressing
+		err = router.Reconcile(canary)
+		require.NoError(t, err)
+
+		hr, err = mocks.meshClient.GatewayapiV1beta1().HTTPRoutes("default").Get(context.TODO(), "podinfo", metav1.GetOptions{})
+		require.NoError(t, err)
+		assert.Len(t, hr.Spec.Rules, 1)
+		assert.Empty(t, cmp.Diff(hr.Spec.Rules[0], rule))
+
+		err = router.SetRoutes(canary, 100, 0, false)
+		hr, err = mocks.meshClient.GatewayapiV1beta1().HTTPRoutes("default").Get(context.TODO(), "podinfo", metav1.GetOptions{})
+		require.NoError(t, err)
+		assert.Len(t, hr.Spec.Rules, 1)
+		assert.Len(t, hr.Spec.Rules[0].Filters, 0)
+	})
 }
 
 func TestGatewayAPIV1Beta1Router_getSessionAffinityRouteRules(t *testing.T) {