Terraform: Parallel builds with Packer

Parellel build is a very useful and important feature of Packer. For example, Packer can build an Amazon AMI and a VMware virtual machine in parallel provisioned with the same scripts, resulting in near-identical images. The AMI can be used for production, the VMware machine can be used for development. Or, another example, if you're using Packer to build software appliances, then you can build the appliance for every supported platform all in parallel and configured from a single template.

‒ https://developer.hashicorp.com/packer/tutorials/docker-get-started/docker-get-started-parallel-builds