provider/aws: allow external ENI attachments

If Terraform creates an ENI and it's attached out of band, Terraform
should not attempt to remove the attachment on subsequent runs.

fixes #2436
fixes #2881

builtin/providers/aws/resource_aws_network_interface.go

@@ -56,6 +56,7 @@ func resourceAwsNetworkInterface() *schema.Resource {
 			"attachment": &schema.Schema{
 				Type:     schema.TypeSet,
 				Optional: true,
+				Computed: true,
 				Elem: &schema.Resource{
 					Schema: map[string]*schema.Schema{
 						"instance": &schema.Schema{

builtin/providers/aws/resource_aws_network_interface_test.go

@@ -57,6 +57,26 @@ func TestAccAWSENI_attached(t *testing.T) {
 	})
 }
 
+func TestAccAWSENI_ignoreExternalAttachment(t *testing.T) {
+	var conf ec2.NetworkInterface
+
+	resource.Test(t, resource.TestCase{
+		PreCheck:     func() { testAccPreCheck(t) },
+		Providers:    testAccProviders,
+		CheckDestroy: testAccCheckAWSENIDestroy,
+		Steps: []resource.TestStep{
+			resource.TestStep{
+				Config: testAccAWSENIConfigExternalAttachment,
+				Check: resource.ComposeTestCheckFunc(
+					testAccCheckAWSENIExists("aws_network_interface.bar", &conf),
+					testAccCheckAWSENIAttributes(&conf),
+					testAccCheckAWSENIMakeExternalAttachment("aws_instance.foo", &conf),
+				),
+			},
+		},
+	})
+}
+
 func TestAccAWSENI_sourceDestCheck(t *testing.T) {
 	var conf ec2.NetworkInterface
 
@@ -211,6 +231,26 @@ func testAccCheckAWSENIDestroy(s *terraform.State) error {
 	return nil
 }
 
+func testAccCheckAWSENIMakeExternalAttachment(n string, conf *ec2.NetworkInterface) resource.TestCheckFunc {
+	return func(s *terraform.State) error {
+		rs, ok := s.RootModule().Resources[n]
+		if !ok || rs.Primary.ID == "" {
+			return fmt.Errorf("Not found: %s", n)
+		}
+		attach_request := &ec2.AttachNetworkInterfaceInput{
+			DeviceIndex:        aws.Int64(2),
+			InstanceID:         aws.String(rs.Primary.ID),
+			NetworkInterfaceID: conf.NetworkInterfaceID,
+		}
+		conn := testAccProvider.Meta().(*AWSClient).ec2conn
+		_, attach_err := conn.AttachNetworkInterface(attach_request)
+		if attach_err != nil {
+			return fmt.Errorf("Error attaching ENI: %s", attach_err)
+		}
+		return nil
+	}
+}
+
 const testAccAWSENIConfig = `
 resource "aws_vpc" "foo" {
     cidr_block = "172.16.0.0/16"
@@ -336,3 +376,56 @@ resource "aws_network_interface" "bar" {
     }
 }
 `
+
+const testAccAWSENIConfigExternalAttachment = `
+resource "aws_vpc" "foo" {
+    cidr_block = "172.16.0.0/16"
+        tags {
+            Name = "tf-eni-test"
+        }
+}
+
+resource "aws_subnet" "foo" {
+    vpc_id = "${aws_vpc.foo.id}"
+    cidr_block = "172.16.10.0/24"
+    availability_zone = "us-west-2a"
+        tags {
+            Name = "tf-eni-test"
+        }
+}
+
+resource "aws_subnet" "bar" {
+    vpc_id = "${aws_vpc.foo.id}"
+    cidr_block = "172.16.11.0/24"
+    availability_zone = "us-west-2a"
+        tags {
+            Name = "tf-eni-test"
+        }
+}
+
+resource "aws_security_group" "foo" {
+  vpc_id = "${aws_vpc.foo.id}"
+  description = "foo"
+  name = "foo"
+}
+
+resource "aws_instance" "foo" {
+    ami = "ami-c5eabbf5"
+    instance_type = "t2.micro"
+    subnet_id = "${aws_subnet.bar.id}"
+    associate_public_ip_address = false
+    private_ip = "172.16.11.50"
+    tags {
+        Name = "tf-eni-test"
+    }
+}
+
+resource "aws_network_interface" "bar" {
+    subnet_id = "${aws_subnet.foo.id}"
+    private_ips = ["172.16.10.100"]
+    security_groups = ["${aws_security_group.foo.id}"]
+    tags {
+        Name = "bar_interface"
+    }
+}
+`