Merge pull request #877 from hashicorp/i-859-ignore-ec2-root-volume

providers/aws: ignore ec2 root devices

builtin/providers/aws/resource_aws_instance.go

@@ -377,11 +377,19 @@ func resourceAwsInstanceRead(d *schema.ResourceData, meta interface{}) error {
 	}
 	d.Set("security_groups", sgs)
 
-	volIDs := make([]string, len(instance.BlockDevices))
-	bdByVolID := make(map[string]ec2.BlockDevice)
-	for i, bd := range instance.BlockDevices {
-		volIDs[i] = bd.VolumeId
-		bdByVolID[bd.VolumeId] = bd
+	blockDevices := make(map[string]ec2.BlockDevice)
+	for _, bd := range instance.BlockDevices {
+		// Skip root device; AWS attaches it automatically and terraform does not
+		// manage it
+		if bd.DeviceName == instance.RootDeviceName {
+			continue
+		}
+		blockDevices[bd.VolumeId] = bd
+	}
+
+	volIDs := make([]string, 0, len(blockDevices))
+	for volID := range blockDevices {
+		volIDs = append(volIDs, volID)
 	}
 
 	volResp, err := ec2conn.Volumes(volIDs, ec2.NewFilter())
@@ -396,11 +404,11 @@ func resourceAwsInstanceRead(d *schema.ResourceData, meta interface{}) error {
 			return err
 		}
 		bds[i] = make(map[string]interface{})
-		bds[i]["device_name"] = bdByVolID[vol.VolumeId].DeviceName
+		bds[i]["device_name"] = blockDevices[vol.VolumeId].DeviceName
 		bds[i]["snapshot_id"] = vol.SnapshotId
 		bds[i]["volume_type"] = vol.VolumeType
 		bds[i]["volume_size"] = volSize
-		bds[i]["delete_on_termination"] = bdByVolID[vol.VolumeId].DeleteOnTermination
+		bds[i]["delete_on_termination"] = blockDevices[vol.VolumeId].DeleteOnTermination
 		bds[i]["encrypted"] = vol.Encrypted
 	}
 	d.Set("block_device", bds)

builtin/providers/aws/resource_aws_instance_test.go

@@ -97,6 +97,11 @@ func TestAccAWSInstance_blockDevicesCheck(t *testing.T) {
 				Check: resource.ComposeTestCheckFunc(
 					testAccCheckInstanceExists(
 						"aws_instance.foo", &v),
+					// though two block devices exist in EC2, terraform state should only
+					// have the one block device we created, as terraform does not manage
+					// the root device
+					resource.TestCheckResourceAttr(
+						"aws_instance.foo", "block_device.#", "1"),
 					testCheck(),
 				),
 			},
@@ -353,9 +358,9 @@ resource "aws_instance" "foo" {
 	ami = "ami-55a7ea65"
 	instance_type = "m1.small"
 	block_device {
-	  device_name = "/dev/sdb"
-	  volume_type = "gp2"
-	  volume_size = 10
+		device_name = "/dev/sdb"
+		volume_type = "gp2"
+		volume_size = 10
 	}
 }
 `