AWS user_data with Packer

Question

So I'm trying to use Packer to create an AWS image and specify some user data via user_data_file. The contents of this file needs to be run when the instance boots as it will be unique each time. I can't bake this into the AMI.

Using packer I have the following:

{
  "variables": {
  "ami_name": ""
  },
  "builders": [
  {
    "type": "amazon-ebs",
    "region": "us-east-1",
    "source_ami": "ami-c8580bdf",
    "instance_type": "t2.micro",
    "ssh_username": "ubuntu",
    "ami_name": "{{ user `ami_name` }}-{{ isotime | clean_ami_name }}",
    "user_data_file": "user_data.sh",
    "tags": {
      "os_version": "ubuntu",
      "built_by": "packer",
      "build_on": "{{ isotime | clean_ami_name }}",
      "Name": "{{ user `ami_name` }}"
    }
  }],
  "provisioners": [
  {
    "type": "ansible",
    "playbook_file": "playbook.yml",
    "user": "ubuntu"
  }]
}

The contents of my user_data shell script are just a few basic config lines for a package that was installed via the ansible scripts that were run in the provisioners step. Watching the output of Packer I can confirm that the ansible scripts all run.

Packer completes and creates the AMI, but the user data piece is never executed. No record of it exists in resulting image. There is no /userdata.log file and /var/lib/cloud/instance/user-data.txt is empty I feel like I missing something basic as this should be a very simple thing to do with Packer.

Answer 1

Rereading this I think maybe you misunderstood how user-data scripts work with Packer.

user_data is provided when the EC2 instance is launched by Packer. This instance is in the end, after provisioning snapshoted and saved as an AMI.

When you launch new instances from the created AMI it doesn't have the same user-data, it gets the user-data you specify when launching this new instance.

The effect of the initial (defined in your template) user-data might or might not be present in the new instance depending if the change was persisted in the AMI.