Packer Cheatsheet

Top commands.

Overview

Packer is HashiCorp’s machine-image builder. The point of the tool is that images are code: HCL templates define builders, provisioners, and post-processors so the same artefact can be reproduced anywhere.

• Image-as-code. Builders, provisioners, and post-processors declared in HCL. Reproducible images, not screenshots of console clicks.
• Multi-cloud builders. AWS AMIs, Azure VHDs, GCP images, Docker, Vagrant boxes. One template can produce all of them.
• Provisioner integration. Shell, Ansible, Chef, Puppet. Existing configuration tooling slots in without rewrite.
• Parallel builds plus verification. Multiple targets built simultaneously; build-time tests fail bad images before deploy.

The approach

The practical workflow is HCL-first, validate before build, and use existing configuration management for provisioning. Five commands cover almost every operator interaction.

• packer init. Install required plugins. Modern Packer needs explicit init; do not skip.
• packer validate. Validate the template before kicking off a long build. Catches typos in seconds, not minutes.
• packer build and build -only. packer build builds every target; -only=aws targets a single builder for fast iteration.
• Provisioner with Ansible. Reuse existing Ansible playbooks for image configuration. The infrastructure code already exists; do not rewrite it.

Why this compounds

The first Packer template takes effort; subsequent images reuse the patterns. Within a year the team has a small image library and a habit of treating images as code.

• Reproducible images. Templates produce consistent images across regions and accounts. Drift between environments shrinks.
• Faster boot times. Pre-baked images boot faster than instances configured via user-data. Production agility improves visibly.
• Reusable templates. Common base images replace duplication. New service images extend a base, not start from scratch.
• Year-one investment, year-two habit. The first template is heavy lift. By the fourth or fifth, the patterns are reflexive.