Packer

Packer builds machine images from a template. A build might start from a Rocky Linux base image, install packages, copy files, run hardening steps, and publish the finished image to a cloud account or image catalogue.

It fits well with immutable infrastructure. Instead of patching a server by hand, you build a new image and replace the old instance.

Packer is often paired with Terraform. Packer creates the image; Terraform launches infrastructure from it. That split keeps image build logic out of deployment code, which makes both sides easier to reason about.