(discoverychain) Add support to disable routes with weight 0 instead of setting it 1 explicitly

Author: sujay-hashicorp

.changelog/23216.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+api-gateway: allow http-routes to set `weight: 0` to disable traffic to particular service
+```

agent/structs/config_entry_routes.go

@@ -105,8 +105,19 @@ func (e *HTTPRouteConfigEntry) Normalize() error {
 			rule.Matches[j] = normalizeHTTPMatch(match)
 		}
 
+		allServicesHaveZeroWeight := true
 		for j, service := range rule.Services {
 			rule.Services[j] = e.normalizeHTTPService(service)
+			if rule.Services[j].Weight != 0 {
+				allServicesHaveZeroWeight = false
+			}
+		}
+		// Preserve historical behavior for routes that omit all service weights by
+		// normalizing them to 1.
+		if allServicesHaveZeroWeight {
+			for j := range rule.Services {
+				rule.Services[j].Weight = 1
+			}
 		}
 		e.Rules[i] = rule
 	}
@@ -123,7 +134,7 @@ func (e *HTTPRouteConfigEntry) Normalize() error {
 func (e *HTTPRouteConfigEntry) normalizeHTTPService(service HTTPService) HTTPService {
 	service.Merge(e.GetEnterpriseMeta())
 	service.Normalize()
-	if service.Weight <= 0 {
+	if service.Weight < 0 {
 		service.Weight = 1
 	}
 	return service

agent/structs/config_entry_routes_test.go

@@ -338,7 +338,7 @@ func TestHTTPRoute(t *testing.T) {
 				}},
 			},
 		},
-		"rule normalizes service weight": {
+		"rule preserves zero service weight and normalizes negative service weight": {
 			entry: &HTTPRouteConfigEntry{
 				Kind: HTTPRoute,
 				Name: "route-one",
@@ -355,6 +355,29 @@ func TestHTTPRoute(t *testing.T) {
 					},
 				}},
 			},
+			check: func(t *testing.T, entry ConfigEntry) {
+				route := entry.(*HTTPRouteConfigEntry)
+				require.Equal(t, 0, route.Rules[0].Services[0].Weight)
+				require.Equal(t, 1, route.Rules[0].Services[1].Weight)
+			},
+		},
+		"rule normalizes all-zero service weights to defaults": {
+			entry: &HTTPRouteConfigEntry{
+				Kind: HTTPRoute,
+				Name: "route-one",
+				Rules: []HTTPRouteRule{{
+					Services: []HTTPService{
+						{
+							Name:   "test",
+							Weight: 0,
+						},
+						{
+							Name:   "test2",
+							Weight: 0,
+						},
+					},
+				}},
+			},
 			check: func(t *testing.T, entry ConfigEntry) {
 				route := entry.(*HTTPRouteConfigEntry)
 				require.Equal(t, 1, route.Rules[0].Services[0].Weight)