In the builders section of the template, we define our build details.
We are using the most common type of AMI builder: amazon-ebs. There are other types of AWS builders, for instance, storage-backed instance types.
Next, we define the type of instance to use when baking.
The source_ami property in this recipe is an AWS Linux AMI ID in the region we have specified. The ssh_username allows you to set the username used to connect and run provisioners on the instance. This will be determined by your operating system, which in our case is ec2-user ...