ensure route parents are unique when creating an http route

agent/structs/config_entry_routes.go

@@ -4,6 +4,7 @@
 package structs
 
 import (
+	"errors"
 	"fmt"
 	"strings"
 
@@ -143,10 +144,16 @@ func (e *HTTPRouteConfigEntry) Validate() error {
 		APIGateway: true,
 	}
 
+	uniques := make(map[ResourceReference]struct{}, len(e.Parents))
+
 	for _, parent := range e.Parents {
 		if !validParentKinds[parent.Kind] {
 			return fmt.Errorf("unsupported parent kind: %q, must be 'api-gateway'", parent.Kind)
 		}
+		if _, ok := uniques[parent]; ok {
+			return errors.New("route parents must be unique")
+		}
+		uniques[parent] = struct{}{}
 	}
 
 	if err := validateConfigEntryMeta(e.Meta); err != nil {