limiting subnetgroup name to alphanumeric and hyphens

builtin/providers/aws/resource_aws_redshift_subnet_group.go

@@ -174,9 +174,9 @@ func subnetIdsToSlice(subnetIds []*redshift.Subnet) []string {
 
 func validateRedshiftSubnetGroupName(v interface{}, k string) (ws []string, errors []error) {
 	value := v.(string)
-	if !regexp.MustCompile(`^[0-9a-z-_]+$`).MatchString(value) {
+	if !regexp.MustCompile(`^[0-9a-z-]+$`).MatchString(value) {
 		errors = append(errors, fmt.Errorf(
-			"only lowercase alphanumeric characters, hyphens, underscores, and periods allowed in %q", k))
+			"only lowercase alphanumeric characters and hyphens allowed in %q", k))
 	}
 	if len(value) > 255 {
 		errors = append(errors, fmt.Errorf(

builtin/providers/aws/resource_aws_redshift_subnet_group_test.go

@@ -79,6 +79,14 @@ func TestResourceAWSRedshiftSubnetGroupNameValidation(t *testing.T) {
 			Value:    "TestingSG",
 			ErrCount: 1,
 		},
+		{
+			Value:    "testing_123",
+			ErrCount: 1,
+		},
+		{
+			Value:    "testing.123",
+			ErrCount: 1,
+		},
 		{
 			Value:    randomString(256),
 			ErrCount: 1,