Backport of NET-2904 Fixes API Gateway Route Service Weight Division Error into release/1.15.x

.changelog/16531.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+gateways: fix HTTPRoute bug where services with a weight not divisible by 10000 are never registered properly
+```

agent/xds/routes.go

@@ -863,6 +863,7 @@ func (s *ResourceGenerator) makeRouteActionForSplitter(
 	forMeshGateway bool,
 ) (*envoy_route_v3.Route_Route, error) {
 	clusters := make([]*envoy_route_v3.WeightedCluster_ClusterWeight, 0, len(splits))
+	totalWeight := 0
 	for _, split := range splits {
 		nextNode := chain.Nodes[split.NextNode]
 
@@ -878,8 +879,10 @@ func (s *ResourceGenerator) makeRouteActionForSplitter(
 
 		// The smallest representable weight is 1/10000 or .01% but envoy
 		// deals with integers so scale everything up by 100x.
+		weight := int(split.Weight * 100)
+		totalWeight += weight
 		cw := &envoy_route_v3.WeightedCluster_ClusterWeight{
-			Weight: makeUint32Value(int(split.Weight * 100)),
+			Weight: makeUint32Value(weight),
 			Name:   targetOptions.clusterName,
 		}
 		if err := injectHeaderManipToWeightedCluster(split.Definition, cw); err != nil {
@@ -893,12 +896,19 @@ func (s *ResourceGenerator) makeRouteActionForSplitter(
 		return nil, fmt.Errorf("number of clusters in splitter must be > 0; got %d", len(clusters))
 	}
 
+	envoyWeightScale := 10000
+	if envoyWeightScale < totalWeight {
+		clusters[0].Weight.Value += uint32(totalWeight - envoyWeightScale)
+	} else {
+		clusters[0].Weight.Value += uint32(envoyWeightScale - totalWeight)
+	}
+
 	return &envoy_route_v3.Route_Route{
 		Route: &envoy_route_v3.RouteAction{
 			ClusterSpecifier: &envoy_route_v3.RouteAction_WeightedClusters{
 				WeightedClusters: &envoy_route_v3.WeightedCluster{
 					Clusters:    clusters,
-					TotalWeight: makeUint32Value(10000), // scaled up 100%
+					TotalWeight: makeUint32Value(envoyWeightScale), // scaled up 100%
 				},
 			},
 		},

test/integration/connect/envoy/case-api-gateway-http-simple/setup.sh

@@ -35,6 +35,10 @@ rules = [
     services = [
       {
         name = "s1"
+      },
+      {
+        name = "s2"
+        weight = 2
       }
     ]
   }

test/integration/connect/envoy/case-api-gateway-http-simple/verify.bats

@@ -22,9 +22,9 @@ load helpers
 }
 
 @test "api gateway should be able to connect to s1 via configured port" {
-  run retry_long curl -s -f -d hello localhost:9999
+  run retry_long curl -s -d hello localhost:9999
   [ "$status" -eq 0 ]
-  [[ "$output" == *"hello"* ]]
+  [[ ! -z "$output" ]]
 }
 
 @test "api gateway should get an intentions error connecting to s2 via configured port" {