Packer

Packer builds machine images so you don't have to. Define your AMI, Docker image, or VM template as code, and Packer creates identical images across AWS, GCP, Azure, VMware, and more from a single config. Immutable infrastructure starts here.

If you're deploying to cloud VMs and want reproducible, version-controlled images, Packer is the standard tool. Docker handles containerized workloads and is the modern default for most teams. Ansible/Chef/Puppet configure existing machines rather than baking images. Cloud-native image builders (EC2 Image Builder, GCP's image tools) exist but lock you into one provider.

The multi-cloud story is Packer's killer feature. One template, images for every cloud. The HCL config language is clean, and the plugin system extends it to basically any target.

The catch: HashiCorp switched Packer to the BSL license in 2023, which means competitors can't offer it as a service. For your own use it's fine, but the license shift spooked the open-source community. Also, if you've gone all-in on containers, you probably don't need Packer at all — Dockerfiles replaced it for many teams.