Replace error from --enable-service-discovery flag with warning

Author: bvtujo

ecs-cli/modules/cli/compose/entity/service/service.go

@@ -347,7 +347,7 @@ func (s *Service) buildUpdateServiceInput(count *int64, serviceName, taskDefinit
 
 func (s *Service) updateService(ecsService *ecs.Service, newTaskDefinition *ecs.TaskDefinition) error {
 	if s.Context().CLIContext.Bool(flags.EnableServiceDiscoveryFlag) {
-		return fmt.Errorf("Service Discovery can not be enabled on an existing ECS Service")
+		log.Warningln("Service Discovery can not be enabled on an existing ECS Service. Skipping this flag...")
 	}
 
 	schedulingStrategy := strings.ToUpper(s.Context().CLIContext.String(flags.SchedulingStrategyFlag))

ecs-cli/modules/cli/compose/entity/service/service_test.go

@@ -1609,8 +1609,10 @@ func TestUpdateExistingServiceWithServiceDiscoveryFlag(t *testing.T) {
 		ServiceName:    aws.String(serviceName),
 	}
 
+	expectedInput := getDefaultUpdateInput()
+	expectedInput.serviceName = serviceName
 	// call tests
-	updateServiceExceptionTest(t, flagSet, &config.CommandConfig{}, &utils.ECSParams{}, existingService)
+	updateServiceTest(t, flagSet, &config.CommandConfig{}, &utils.ECSParams{}, expectedInput, existingService, true)
 }
 
 ///////////////////////////////////////