provider/aws: Support refresh of EC2 instance user_data.

Make sure to hash base64 decoded value since user_data might be given
either raw bytes or base64 value.

This helps https://github.com/hashicorp/terraform/issues/1887 somewhat
as now you can:

1) Update user_data in AWS console.
2) Respectively update user_data in terraform code.
3) Just refresh terraform state and it should not report any changes.

builtin/providers/aws/resource_aws_instance.go

@@ -98,8 +98,7 @@ func resourceAwsInstance() *schema.Resource {
 				StateFunc: func(v interface{}) string {
 					switch v.(type) {
 					case string:
-						hash := sha1.Sum([]byte(v.(string)))
+						return userDataHashSum(v.(string))
-						return hex.EncodeToString(hash[:])
 					default:
 						return ""
 					}
@@ -583,6 +582,18 @@ func resourceAwsInstanceRead(d *schema.ResourceData, meta interface{}) error {
 		}
 		d.Set("disable_api_termination", attr.DisableApiTermination.Value)
 	}
+	{
+		attr, err := conn.DescribeInstanceAttribute(&ec2.DescribeInstanceAttributeInput{
+			Attribute:  aws.String(ec2.InstanceAttributeNameUserData),
+			InstanceId: aws.String(d.Id()),
+		})
+		if err != nil {
+			return err
+		}
+		if attr.UserData.Value != nil {
+			d.Set("user_data", userDataHashSum(*attr.UserData.Value))
+		}
+	}
 
 	return nil
 }
@@ -1166,3 +1177,16 @@ func iamInstanceProfileArnToName(ip *ec2.IamInstanceProfile) string {
 	parts := strings.Split(*ip.Arn, "/")
 	return parts[len(parts)-1]
 }
+
+func userDataHashSum(user_data string) string {
+	// Check whether the user_data is not Base64 encoded.
+	// Always calculate hash of base64 decoded value since we
+	// check against double-encoding when setting it
+	v, base64DecodeError := base64.StdEncoding.DecodeString(user_data)
+	if base64DecodeError != nil {
+		v = []byte(user_data)
+	}
+
+	hash := sha1.Sum(v)
+	return hex.EncodeToString(hash[:])
+}

builtin/providers/aws/resource_aws_instance_test.go

@@ -39,7 +39,7 @@ func TestAccAWSInstance_basic(t *testing.T) {
 		// we'll import as VPC security groups, which is fine. We verify
 		// VPC security group import in other tests
 		IDRefreshName:   "aws_instance.foo",
-		IDRefreshIgnore: []string{"user_data", "security_groups", "vpc_security_group_ids"},
+		IDRefreshIgnore: []string{"security_groups", "vpc_security_group_ids"},
 
 		Providers:    testAccProviders,
 		CheckDestroy: testAccCheckInstanceDestroy,
@@ -195,7 +195,7 @@ func TestAccAWSInstance_blockDevices(t *testing.T) {
 		PreCheck:      func() { testAccPreCheck(t) },
 		IDRefreshName: "aws_instance.foo",
 		IDRefreshIgnore: []string{
-			"ephemeral_block_device", "user_data", "security_groups", "vpc_security_groups"},
+			"ephemeral_block_device", "security_groups", "vpc_security_groups"},
 		Providers:    testAccProviders,
 		CheckDestroy: testAccCheckInstanceDestroy,
 		Steps: []resource.TestStep{
@@ -346,7 +346,7 @@ func TestAccAWSInstance_vpc(t *testing.T) {
 	resource.Test(t, resource.TestCase{
 		PreCheck:        func() { testAccPreCheck(t) },
 		IDRefreshName:   "aws_instance.foo",
-		IDRefreshIgnore: []string{"associate_public_ip_address", "user_data"},
+		IDRefreshIgnore: []string{"associate_public_ip_address"},
 		Providers:       testAccProviders,
 		CheckDestroy:    testAccCheckInstanceDestroy,
 		Steps: []resource.TestStep{
@@ -358,7 +358,7 @@ func TestAccAWSInstance_vpc(t *testing.T) {
 					resource.TestCheckResourceAttr(
 						"aws_instance.foo",
 						"user_data",
-						"2fad308761514d9d73c3c7fdc877607e06cf950d"),
+						"562a3e32810edf6ff09994f050f12e799452379d"),
 				),
 			},
 		},