Use engine_version and engine_version_actual.

aws/resource_aws_db_instance.go

@@ -86,10 +86,14 @@ func resourceAwsDbInstance() *schema.Resource {
 			},
 
 			"engine_version": {
-				Type:             schema.TypeString,
-				Optional:         true,
-				Computed:         true,
-				DiffSuppressFunc: suppressAwsDbEngineVersionDiffs,
+				Type:     schema.TypeString,
+				Optional: true,
+				Computed: true,
+			},
+
+			"engine_version_actual": {
+				Type:     schema.TypeString,
+				Computed: true,
 			},
 
 			"ca_cert_identifier": {
@@ -1407,7 +1411,6 @@ func resourceAwsDbInstanceRead(d *schema.ResourceData, meta interface{}) error {
 	d.Set("username", v.MasterUsername)
 	d.Set("deletion_protection", v.DeletionProtection)
 	d.Set("engine", v.Engine)
-	d.Set("engine_version", v.EngineVersion)
 	d.Set("allocated_storage", v.AllocatedStorage)
 	d.Set("iops", v.Iops)
 	d.Set("copy_tags_to_snapshot", v.CopyTagsToSnapshot)
@@ -1433,6 +1436,8 @@ func resourceAwsDbInstanceRead(d *schema.ResourceData, meta interface{}) error {
 		d.Set("db_subnet_group_name", v.DBSubnetGroup.DBSubnetGroupName)
 	}
 
+	dbSetResourceDataEngineVersionFromInstance(d, v)
+
 	if v.CharacterSetName != nil {
 		d.Set("character_set_name", v.CharacterSetName)
 	}
@@ -1993,3 +1998,12 @@ func expandRestoreToPointInTime(l []interface{}) *rds.RestoreDBInstanceToPointIn
 
 	return input
 }
+
+func dbSetResourceDataEngineVersionFromInstance(d *schema.ResourceData, c *rds.DBInstance) {
+	oldVersion := d.Get("engine_version").(string)
+	newVersion := aws.StringValue(c.EngineVersion)
+	if oldVersion != newVersion && string(append([]byte(oldVersion), []byte(".")...)) != string([]byte(newVersion)[0:len(oldVersion)+1]) {
+		d.Set("engine_version", newVersion)
+	}
+	d.Set("engine_version_actual", newVersion)
+}

aws/resource_aws_db_instance_test.go

@@ -116,6 +116,39 @@ func TestAccAWSDBInstance_basic(t *testing.T) {
 	})
 }
 
+func TestAccAWSDBInstance_OnlyMajorVersion(t *testing.T) {
+	var dbInstance1 rds.DBInstance
+	resourceName := "aws_db_instance.test"
+	engine := "mysql"
+	engineVersion1 := "5.6"
+
+	resource.ParallelTest(t, resource.TestCase{
+		PreCheck:     func() { testAccPreCheck(t) },
+		ErrorCheck:   testAccErrorCheck(t, rds.EndpointsID),
+		Providers:    testAccProviders,
+		CheckDestroy: testAccCheckAWSClusterDestroy,
+		Steps: []resource.TestStep{
+			{
+				Config: testAccAWSDBInstanceConfig_MajorVersionOnly(engine, engineVersion1),
+				Check: resource.ComposeTestCheckFunc(
+					testAccCheckAWSDBInstanceExists(resourceName, &dbInstance1),
+					resource.TestCheckResourceAttr(resourceName, "engine", engine),
+					resource.TestCheckResourceAttr(resourceName, "engine_version", engineVersion1),
+				),
+			},
+			{
+				ResourceName:      resourceName,
+				ImportState:       true,
+				ImportStateVerify: true,
+				ImportStateVerifyIgnore: []string{
+					"engine_version",
+					"password",
+				},
+			},
+		},
+	})
+}
+
 func TestAccAWSDBInstance_namePrefix(t *testing.T) {
 	var v rds.DBInstance
 
@@ -3281,6 +3314,28 @@ resource "aws_db_instance" "bar" {
 `)
 }
 
+func testAccAWSDBInstanceConfig_MajorVersionOnly(engine, engineVersion string) string {
+	return composeConfig(testAccAWSDBInstanceConfig_orderableClassMysql(), fmt.Sprintf(`
+resource "aws_db_instance" "test" {
+  allocated_storage       = 10
+  backup_retention_period = 0
+  engine                  = %[1]q
+  engine_version          = %[2]q
+  instance_class          = "db.r4.large"
+  name                    = "baz"
+  parameter_group_name    = "default.mysql5.6"
+  password                = "barbarbarbar"
+  skip_final_snapshot     = true
+  username                = "foo"
+
+  # Maintenance Window is stored in lower case in the API, though not strictly
+  # documented. Terraform will downcase this to match (as opposed to throw a
+  # validation error).
+  maintenance_window = "Fri:09:00-Fri:09:30"
+}
+`, engine, engineVersion))
+}
+
 func testAccAWSDBInstanceConfig_namePrefix() string {
 	return composeConfig(testAccAWSDBInstanceConfig_orderableClassMysql(), `
 resource "aws_db_instance" "test" {

website/docs/r/db_instance.html.markdown

@@ -116,8 +116,8 @@ For information on the difference between the available Aurora MySQL engines
 see [Comparison between Aurora MySQL 1 and Aurora MySQL 2](https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/AuroraMySQL.Updates.20180206.html)
 in the Amazon RDS User Guide.
 * `engine_version` - (Optional) The engine version to use. If `auto_minor_version_upgrade`
-is enabled, you can provide a prefix of the version such as `5.7` (for `5.7.10`) and
-this attribute will ignore differences in the patch version automatically (e.g. `5.7.17`).
+is enabled, you can provide a prefix of the version such as `5.7` (for `5.7.10`).
+The actual engine version used is returned in the attribute `engine_version_actual`, [defined below](#engine_version_actual).
 For supported values, see the EngineVersion parameter in [API action CreateDBInstance](https://docs.aws.amazon.com/AmazonRDS/latest/APIReference/API_CreateDBInstance.html).
 Note that for Amazon Aurora instances the engine version must match the [DB cluster](/docs/providers/aws/r/rds_cluster.html)'s engine version'.
 * `final_snapshot_identifier` - (Optional) The name of your final DB snapshot
@@ -279,7 +279,7 @@ DB instance.
 * `domain_iam_role_name` - The name of the IAM role to be used when making API calls to the Directory Service.
 * `endpoint` - The connection endpoint in `address:port` format.
 * `engine` - The database engine.
-* `engine_version` - The database engine version.
+* `engine_version_actual` - The running version of the database.
 * `hosted_zone_id` - The canonical hosted zone ID of the DB instance (to be used
 in a Route 53 Alias record).
 * `id` - The RDS instance ID.