Packer vs Docker: Machine Images vs Containers
Packer builds machine images (AMIs, VM images) for many platforms; Docker builds container images - different artifacts for different deployment targets.
Packer (HashiCorp) automates building identical machine images - AMIs, Azure images, VM images - from a single source config across multiple platforms. Docker builds container images run by a container engine. They are not competitors so much as tools for different artifact types: full machine images vs layered containers.
| Packer | Docker | |
|---|---|---|
| Artifact | Machine images (AMI, VM) | Container images |
| Target | VMs, cloud instances | Container runtimes |
| Boot model | Full OS image | Process in container |
| Multi-platform | Many builders | OCI registries |
| Best for | Golden VM/AMI images | Containerized apps |
In CI
Use Docker when you ship containers to a runtime or Kubernetes. Use Packer when you bake golden VM or cloud images - for example pre-installing tooling into an AMI so instances boot ready. Many pipelines use both: Packer for the base instance image and Docker for the app inside it. Pick by what your infrastructure actually runs.
Speed it up
Both image builds are heavy. Cache layers (Docker) and reuse base images (Packer), and run the builds in CI. Faster managed runners shorten these long-running image bakes.
The verdict
Deploying containers: Docker. Baking VM/cloud machine images (AMIs): Packer. They target different artifacts and often work together - Packer for the host image, Docker for the app.