provider/aws: Fix issue with AWS RDS DB instance which prevented disabling backups

builtin/providers/aws/resource_aws_db_instance.go

@@ -13,6 +13,12 @@ import (
 	"github.com/hashicorp/terraform/helper/schema"
 )
 
+// Establish a sentinel value to allow Backup Rention to 0, disabling backups of
+// the RDS Instance. This is needed to distinguish between a zero value in the
+// configuration, or no value provided. The default on AWS is 1 (one day).
+// See http://docs.aws.amazon.com/AmazonRDS/latest/APIReference/API_CreateDBInstance.html
+const backupRetentionPeriodUnset = -1
+
 func resourceAwsDbInstance() *schema.Resource {
 	return &schema.Resource{
 		Create: resourceAwsDbInstanceCreate,
@@ -87,6 +93,7 @@ func resourceAwsDbInstance() *schema.Resource {
 				Optional: true,
 				Computed: true,
 				ForceNew: true,
+				Default:  backupRetentionPeriodUnset,
 			},
 
 			"backup_window": &schema.Schema{
@@ -201,8 +208,11 @@ func resourceAwsDbInstanceCreate(d *schema.ResourceData, meta interface{}) error
 		opts.StorageType = aws.String(attr.(string))
 	}
 
-	if attr, ok := d.GetOk("backup_retention_period"); ok {
-		opts.BackupRetentionPeriod = aws.Integer(attr.(int))
+	// Compare the backup_retention_period value to the Default. This allows a
+	// zero value for backup_retention_period, disabling backups.
+	brp := d.Get("backup_retention_period")
+	if brp != backupRetentionPeriodUnset {
+		opts.BackupRetentionPeriod = aws.Integer(brp.(int))
 	}
 
 	if attr, ok := d.GetOk("iops"); ok {

builtin/providers/aws/resource_aws_db_instance_test.go

@@ -141,6 +141,8 @@ resource "aws_db_instance" "bar" {
 	password = "barbarbarbar"
 	username = "foo"
 
+	backup_retention_period = 0
+
 	parameter_group_name = "default.mysql5.6"
 }
 `