resource/aws_ssm_maintenance_window_task: Prevent ValidationException…

… error on update when priority is not set or 0 (#17885)

Reference: #17871

Priority is optional, but it is currently configured in every test configuration which is why this was not found before. To minimize the changes to verify this bug and timebox effort as part of triage, submitting one preferred style test that covers the behavior.

Previously:

```
=== CONT  TestAccAWSSSMMaintenanceWindowTask_Description
    resource_aws_ssm_maintenance_window_task_test.go:114: Step 3/3 error: Error running apply: exit status 1

        Error: Error updating Maintenance Window (mw-02f66f1bc3df08b83) Task (4c1a1e3e-c449-4e2d-882c-5f8a23a2104d): ValidationException: Value null at 'Priority' failed to satisfy constraint: Member must not be null
        	status code: 400, request id: fc15f736-7e53-49bb-8d5d-11f35ba98a30

          on terraform_plugin_test.tf line 58, in resource "aws_ssm_maintenance_window_task" "test":
          58: resource "aws_ssm_maintenance_window_task" "test" {

--- FAIL: TestAccAWSSSMMaintenanceWindowTask_Description (22.29s)
```

Output from acceptance testing in AWS Commercial:

```
--- PASS: TestAccAWSSSMMaintenanceWindowTask_basic (36.64s)
--- PASS: TestAccAWSSSMMaintenanceWindowTask_Description (36.65s)
--- PASS: TestAccAWSSSMMaintenanceWindowTask_disappears (20.12s)
--- PASS: TestAccAWSSSMMaintenanceWindowTask_emptyNotificationConfig (21.04s)
--- PASS: TestAccAWSSSMMaintenanceWindowTask_noRole (21.13s)
--- PASS: TestAccAWSSSMMaintenanceWindowTask_TaskInvocationAutomationParameters (49.73s)
--- PASS: TestAccAWSSSMMaintenanceWindowTask_TaskInvocationLambdaParameters (39.99s)
--- PASS: TestAccAWSSSMMaintenanceWindowTask_TaskInvocationRunCommandParameters (50.76s)
--- PASS: TestAccAWSSSMMaintenanceWindowTask_TaskInvocationRunCommandParametersCloudWatch (53.64s)
--- PASS: TestAccAWSSSMMaintenanceWindowTask_TaskInvocationStepFunctionParameters (23.05s)
--- PASS: TestAccAWSSSMMaintenanceWindowTask_updateForcesNewResource (36.64s)
```

Output from acceptance testing in AWS GovCloud (US):

```
--- PASS: TestAccAWSSSMMaintenanceWindowTask_basic (48.68s)
--- PASS: TestAccAWSSSMMaintenanceWindowTask_Description (45.57s)
--- PASS: TestAccAWSSSMMaintenanceWindowTask_disappears (28.64s)
--- PASS: TestAccAWSSSMMaintenanceWindowTask_emptyNotificationConfig (28.72s)
--- PASS: TestAccAWSSSMMaintenanceWindowTask_noRole (28.97s)
--- PASS: TestAccAWSSSMMaintenanceWindowTask_TaskInvocationAutomationParameters (52.58s)
--- PASS: TestAccAWSSSMMaintenanceWindowTask_TaskInvocationLambdaParameters (49.44s)
--- PASS: TestAccAWSSSMMaintenanceWindowTask_TaskInvocationRunCommandParameters (54.30s)
--- PASS: TestAccAWSSSMMaintenanceWindowTask_TaskInvocationRunCommandParametersCloudWatch (60.93s)
--- PASS: TestAccAWSSSMMaintenanceWindowTask_TaskInvocationStepFunctionParameters (31.03s)
--- PASS: TestAccAWSSSMMaintenanceWindowTask_updateForcesNewResource (46.25s)
```

.changelog/17885.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+resource/aws_ssm_maintenance_window_task: Prevent `ValidationException` error on update when priority is not set or 0
+```

aws/resource_aws_ssm_maintenance_window_task.go

@@ -739,6 +739,7 @@ func resourceAwsSsmMaintenanceWindowTaskUpdate(d *schema.ResourceData, meta inte
 	windowID := d.Get("window_id").(string)
 
 	params := &ssm.UpdateMaintenanceWindowTaskInput{
+		Priority:       aws.Int64(int64(d.Get("priority").(int))),
 		WindowId:       aws.String(windowID),
 		WindowTaskId:   aws.String(d.Id()),
 		MaxConcurrency: aws.String(d.Get("max_concurrency").(string)),
@@ -760,10 +761,6 @@ func resourceAwsSsmMaintenanceWindowTaskUpdate(d *schema.ResourceData, meta inte
 		params.Description = aws.String(v.(string))
 	}
 
-	if v, ok := d.GetOk("priority"); ok {
-		params.Priority = aws.Int64(int64(v.(int)))
-	}
-
 	if v, ok := d.GetOk("task_invocation_parameters"); ok {
 		params.TaskInvocationParameters = expandAwsSsmTaskInvocationParameters(v.([]interface{}))
 	}

aws/resource_aws_ssm_maintenance_window_task_test.go

@@ -106,6 +106,41 @@ func TestAccAWSSSMMaintenanceWindowTask_updateForcesNewResource(t *testing.T) {
 	})
 }
 
+func TestAccAWSSSMMaintenanceWindowTask_Description(t *testing.T) {
+	var task1, task2 ssm.MaintenanceWindowTask
+	resourceName := "aws_ssm_maintenance_window_task.test"
+	rName := acctest.RandomWithPrefix("tf-acc-test")
+
+	resource.ParallelTest(t, resource.TestCase{
+		PreCheck:     func() { testAccPreCheck(t) },
+		Providers:    testAccProviders,
+		CheckDestroy: testAccCheckAWSSSMMaintenanceWindowTaskDestroy,
+		Steps: []resource.TestStep{
+			{
+				Config: testAccAWSSSMMaintenanceWindowTaskConfigDescription(rName, "description1"),
+				Check: resource.ComposeTestCheckFunc(
+					testAccCheckAWSSSMMaintenanceWindowTaskExists(resourceName, &task1),
+					resource.TestCheckResourceAttr(resourceName, "description", "description1"),
+				),
+			},
+			{
+				ResourceName:      resourceName,
+				ImportState:       true,
+				ImportStateIdFunc: testAccAWSSSMMaintenanceWindowTaskImportStateIdFunc(resourceName),
+				ImportStateVerify: true,
+			},
+			{
+				Config: testAccAWSSSMMaintenanceWindowTaskConfigDescription(rName, "description2"),
+				Check: resource.ComposeTestCheckFunc(
+					testAccCheckAWSSSMMaintenanceWindowTaskExists(resourceName, &task2),
+					resource.TestCheckResourceAttr(resourceName, "description", "description2"),
+					testAccCheckAwsSsmWindowsTaskNotRecreated(t, &task1, &task2),
+				),
+			},
+		},
+	})
+}
+
 func TestAccAWSSSMMaintenanceWindowTask_TaskInvocationAutomationParameters(t *testing.T) {
 	var task ssm.MaintenanceWindowTask
 	resourceName := "aws_ssm_maintenance_window_task.test"
@@ -614,6 +649,35 @@ resource "aws_ssm_maintenance_window_task" "test" {
 `)
 }
 
+func testAccAWSSSMMaintenanceWindowTaskConfigDescription(rName string, description string) string {
+	return composeConfig(
+		testAccAWSSSMMaintenanceWindowTaskConfigBase(rName),
+		fmt.Sprintf(`
+resource "aws_ssm_maintenance_window_task" "test" {
+  description     = %[1]q
+  max_concurrency = 2
+  max_errors      = 1
+  task_arn        = "AWS-RunShellScript"
+  task_type       = "RUN_COMMAND"
+  window_id       = aws_ssm_maintenance_window.test.id
+
+  targets {
+    key    = "WindowTargetIds"
+    values = [aws_ssm_maintenance_window_target.test.id]
+  }
+
+  task_invocation_parameters {
+    run_command_parameters {
+      parameter {
+        name   = "commands"
+        values = ["pwd"]
+      }
+    }
+  }
+}
+`, description))
+}
+
 func testAccAWSSSMMaintenanceWindowTaskConfigEmptyNotifcationConfig(rName string) string {
 	return fmt.Sprintf(testAccAWSSSMMaintenanceWindowTaskConfigBase(rName) + `