service/rds: Address PR #5010 feedback

* Note aws_rds_cluster engine_version updates will cause an outage
* Revert aws_rds_cluster source_engine_version ForceNew
* Revert aws_rds_cluster_instance ForceNew
* Remove engine and engine_version from testAccAWSClusterConfig_EngineVersionWithPrimaryInstance

aws/resource_aws_rds_cluster.go

@@ -140,7 +140,6 @@ func resourceAwsRDSCluster() *schema.Resource {
 			"engine_version": {
 				Type:     schema.TypeString,
 				Optional: true,
-				ForceNew: false,
 				Computed: true,
 			},
 
@@ -231,7 +230,7 @@ func resourceAwsRDSCluster() *schema.Resource {
 						"source_engine_version": {
 							Type:     schema.TypeString,
 							Required: true,
-							ForceNew: false,
+							ForceNew: true,
 						},
 					},
 				},

aws/resource_aws_rds_cluster_instance.go

@@ -101,7 +101,7 @@ func resourceAwsRDSClusterInstance() *schema.Resource {
 			"engine_version": {
 				Type:     schema.TypeString,
 				Optional: true,
-				ForceNew: false,
+				ForceNew: true,
 				Computed: true,
 			},
 

aws/resource_aws_rds_cluster_test.go

@@ -1557,38 +1557,25 @@ func testAccAWSClusterConfig_EngineVersionWithPrimaryInstance(rInt int, engine,
 
 data "aws_availability_zones" "available" {}
 
-variable "cluster_identifier" {
-  default = "tf-acc-test-%d"
-}
-
-variable "engine" {
-  default = "%s"
-}
-
-variable "engine_version" {
-  default = "%s"
-}
-
 resource "aws_rds_cluster" "test" {
   availability_zones              = ["${data.aws_availability_zones.available.names}"]
-  cluster_identifier              = "${var.cluster_identifier}"
+  cluster_identifier              = "tf-acc-test-%d"
   database_name                   = "mydb"
   db_cluster_parameter_group_name = "default.aurora-postgresql9.6"
-  engine                          = "${var.engine}"
-  engine_version                  = "${var.engine_version}"
+  engine                          = %q
+  engine_version                  = %q
   master_password                 = "mustbeeightcharaters"
   master_username                 = "foo"
   skip_final_snapshot             = true
   apply_immediately               = true
 }
 
 resource "aws_rds_cluster_instance" "test" {
-  identifier         = "${var.cluster_identifier}"
+  identifier         = "tf-acc-test-%d"
   cluster_identifier = "${aws_rds_cluster.test.cluster_identifier}"
-  engine             = "${var.engine}"
-  engine_version     = "${var.engine_version}"
+  engine             = "${aws_rds_cluster.test.engine}"
   instance_class     = "db.r4.large"
-}`, rInt, engine, engineVersion)
+}`, rInt, engine, engineVersion, rInt)
 }
 
 func testAccAWSClusterConfig_Port(rInt, port int) string {

website/docs/r/rds_cluster.html.markdown

@@ -115,7 +115,7 @@ Default: A 30-minute window selected at random from an 8-hour block of time per
 * `iam_database_authentication_enabled` - (Optional) Specifies whether or mappings of AWS Identity and Access Management (IAM) accounts to database accounts is enabled. Please see [AWS Documentation][6] for availability and limitations.
 * `engine` - (Optional) The name of the database engine to be used for this DB cluster. Defaults to `aurora`. Valid Values: `aurora`, `aurora-mysql`, `aurora-postgresql`
 * `engine_mode` - (Optional) The database engine mode. Valid values: `parallelquery`, `provisioned`, `serverless`. Defaults to: `provisioned`. See the [RDS User Guide](https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/aurora-serverless.html) for limitations when using `serverless`.
-* `engine_version` - (Optional) The database engine version.
+* `engine_version` - (Optional) The database engine version. Updating this argument results in an outage.
 * `source_region` - (Optional) The source region for an encrypted replica DB cluster.
 * `enabled_cloudwatch_logs_exports` - (Optional) List of log types to export to cloudwatch. If omitted, no logs will be exported.
    The following log types are supported: `audit`, `error`, `general`, `slowquery`.