aws-user-data-ec2-attach-eni

User data shell script to have an AWS EC2 instance attach an existing ENI (Elastic Network Interface) at creation time. This script is intented for Ubuntu machines as it also configures the new interface. Amazon linuz instances do not need this extra config step.

Requirements

• IAM: The EC2 instance must be authorized to attach the ENI. Make sure you assign it the right role. Below an example of IAM permissions required.
• OS: Currently this script OS target is Ubuntu 16.04. Not tested outside this target.

IAM permissions

Create an EC2 instance role and attach the following policy document

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "AllowAllAttachENI",
            "Effect": "Allow",
            "Action": [
                "ec2:DetachNetworkInterface",
                "ec2:DescribeNetworkInterfaces",
                "ec2:AttachNetworkInterface"
            ],
            "Resource": "*"
        }
    ]
}

Configure

• Replace the variables located at the top of the script, with your own values.
• Copy/paste the script to the User Data section of your instances. (or your Auto-scalling group config, Cloudformation, Terraform scripts, etc...)

Troubleshoot

• User data script is located under the EC2 instance at the following path: /var/lib/cloud/instances/[instance-id]/user-data.txt
• User data script execution log is located under the EC2 instance in the file: /var/log/cloud-init-output.log