resource/aws_launch_configuration: Fix regression from version 2.22.0…

… with instance store AMIs returning an unexpected error (#9810)

New test prior to fix:

```
--- FAIL: TestAccAWSLaunchConfiguration_withInstanceStoreAMI (13.84s)
    testing.go:640: Step 0 error: errors during apply:

        Error: Instance store backed AMIs do not provide a root device name - Use an EBS AMI
```

Output from acceptance testing:

```
--- PASS: TestAccAWSLaunchConfiguration_withSpotPrice (19.05s)
--- PASS: TestAccAWSLaunchConfiguration_withInstanceStoreAMI (20.40s)
--- PASS: TestAccAWSLaunchConfiguration_withBlockDevices (20.90s)
--- PASS: TestAccAWSLaunchConfiguration_withEncryption (21.66s)
--- PASS: TestAccAWSLaunchConfiguration_ebs_noDevice (21.67s)
--- PASS: TestAccAWSLaunchConfiguration_withIAMProfile (29.41s)
--- PASS: TestAccAWSLaunchConfiguration_encryptedRootBlockDevice (34.32s)
--- PASS: TestAccAWSLaunchConfiguration_basic (35.35s)
--- PASS: TestAccAWSLaunchConfiguration_userData (37.26s)
--- PASS: TestAccAWSLaunchConfiguration_updateEbsBlockDevices (37.48s)
--- PASS: TestAccAWSLaunchConfiguration_updateRootBlockDevice (39.25s)
--- PASS: TestAccAWSLaunchConfiguration_withVpcClassicLink (39.58s)
```

aws/resource_aws_instance.go

@@ -1433,7 +1433,7 @@ func fetchRootDeviceName(ami string, conn *ec2.EC2) (*string, error) {
 
 	// Instance store backed AMIs do not provide a root device name.
 	if *image.RootDeviceType == ec2.DeviceTypeInstanceStore {
-		return nil, fmt.Errorf("Instance store backed AMIs do not provide a root device name - Use an EBS AMI")
+		return nil, nil
 	}
 
 	// Some AMIs have a RootDeviceName like "/dev/sda1" that does not appear as a
@@ -1642,15 +1642,20 @@ func readBlockDeviceMappingsFromConfig(
 				log.Print("[WARN] IOPs is only valid for storate type io1 for EBS Volumes")
 			}
 
-			dn, err := fetchRootDeviceName(d.Get("ami").(string), conn)
-			if err != nil {
-				return nil, fmt.Errorf("Expected 1 AMI for ID: %s (%s)", d.Get("ami").(string), err)
-			}
+			if dn, err := fetchRootDeviceName(d.Get("ami").(string), conn); err == nil {
+				if dn == nil {
+					return nil, fmt.Errorf(
+						"Expected 1 AMI for ID: %s, got none",
+						d.Get("ami").(string))
+				}
 
-			blockDevices = append(blockDevices, &ec2.BlockDeviceMapping{
-				DeviceName: dn,
-				Ebs:        ebs,
-			})
+				blockDevices = append(blockDevices, &ec2.BlockDeviceMapping{
+					DeviceName: dn,
+					Ebs:        ebs,
+				})
+			} else {
+				return nil, err
+			}
 		}
 	}
 

aws/resource_aws_launch_configuration_test.go

@@ -127,6 +127,25 @@ func TestAccAWSLaunchConfiguration_withBlockDevices(t *testing.T) {
 	})
 }
 
+func TestAccAWSLaunchConfiguration_withInstanceStoreAMI(t *testing.T) {
+	var conf autoscaling.LaunchConfiguration
+	rInt := acctest.RandInt()
+
+	resource.ParallelTest(t, resource.TestCase{
+		PreCheck:     func() { testAccPreCheck(t) },
+		Providers:    testAccProviders,
+		CheckDestroy: testAccCheckAWSLaunchConfigurationDestroy,
+		Steps: []resource.TestStep{
+			{
+				Config: testAccAWSLaunchConfigurationConfigWithInstanceStoreAMI(rInt),
+				Check: resource.ComposeTestCheckFunc(
+					testAccCheckAWSLaunchConfigurationExists("aws_launch_configuration.bar", &conf),
+				),
+			},
+		},
+	})
+}
+
 func TestAccAWSLaunchConfiguration_updateRootBlockDevice(t *testing.T) {
 	var conf autoscaling.LaunchConfiguration
 	resourceName := "aws_launch_configuration.test"
@@ -549,6 +568,35 @@ data "aws_ami" "ubuntu" {
 `)
 }
 
+func testAccAWSLaunchConfigurationConfig_instanceStoreAMI() string {
+	return fmt.Sprintf(`
+data "aws_ami" "ubuntu_instance_store" {
+  most_recent = true
+  owners      = ["099720109477"] # Canonical
+
+  # Latest Ubuntu 18.04 LTS amd64 instance-store HVM AMI
+  filter {
+    name   = "name"
+    values = ["ubuntu/images/hvm-instance/ubuntu-bionic-18.04-amd64-server*"]
+  }
+}
+`)
+}
+
+func testAccAWSLaunchConfigurationConfigWithInstanceStoreAMI(rInt int) string {
+	return testAccAWSLaunchConfigurationConfig_instanceStoreAMI() + fmt.Sprintf(`
+resource "aws_launch_configuration" "bar" {
+  name_prefix = "tf-acc-test-%d"
+  image_id = "${data.aws_ami.ubuntu_instance_store.id}"
+
+	# When the instance type is updated, the new type must support ephemeral storage.
+  instance_type = "m1.small"
+  user_data = "foobar-user-data"
+  associate_public_ip_address = false
+}
+`, rInt)
+}
+
 func testAccAWSLaunchConfigurationConfigWithRootBlockDevice(rInt int) string {
 	return testAccAWSLaunchConfigurationConfig_ami() + fmt.Sprintf(`
 resource "aws_launch_configuration" "test" {