Building instance images with Packer

Considering our example application is already stateless, we can proceed with building an immutable infrastructure on top of it. Since the artifacts Packer generates are VM images, we have to decide on the format and the builder we would like to use.
Let's focus our example on Amazon Web Services, while keeping in mind that a similar approach will also work with other supported providers. A simple Packer template may look like this:

{
  "variables": {
    "aws_access_key": "",
    "aws_secret_key": ""
  },
  "builders": [{
    "type": "amazon-ebs",
    "access_key": "{{user `aws_access_key`}}",
    "secret_key": "{{user `aws_secret_key`}}",
    "region": "eu-central-1",
    "source_ami": "ami-0f1026b68319bad6c",
    "instance_type": "t2.micro",
    "ssh_username": &quot...