Kamal

What Kamal is

Kamal is a free deployment tool from 37signals for running containerized web apps in production. It uses Docker to deploy to servers ranging from bare metal machines to cloud VMs, and works with any web app that can be containerized. Although originally built for Rails apps, Kamal is not limited to Rails. Its listed deployment features include zero-downtime deploys, rolling restarts, asset bridging, remote builds, and accessory service management. Rolling rollouts, deployment rollback, and an audit log are also listed.

To get started, provide server IP addresses and connect over SSH. The `kamal setup` command can install Docker when needed, build and push the app image, and start the app on the servers. Docker Hub is the default image registry; the documentation also describes local registries, AWS ECR, and GCP Artifact Registry. Secret-fetching helpers support 1Password, LastPass, Bitwarden, Bitwarden Secrets Manager, AWS Secrets Manager, Doppler, GCP Secret Manager, and Passbolt. Secrets go into an env file on the host rather than directly into the container, and the docs advise keeping `.kamal/secrets` out of version control. Custom scripts can run at selected deployment points; a non-zero exit code stops the command. Kamal runs on Linux and macOS. It can be installed globally with Ruby using `gem install kamal`, or run in a Docker container with some limitations.

Who it suits

Kamal suits developers and operators who can work with basic Linux or Docker concepts and want to deploy containerized web apps to their own servers. It supports Rails and other containerizable web apps, with deployment targets including bare metal and cloud VMs.

Limits

Kamal has no paid plan listed; the Kamal plan is free. Deployment to multiple servers requires a load balancer in front of them, and the Docker container installation route has some limitations.

Getting started

1. Visit https://kamal-deploy.org/.
2. Install Ruby, then install Kamal globally with `gem install kamal`, or use its Docker installation route with the documented limitations.
3. Provide server IP addresses and connect over SSH with an SSH key.
4. Run `kamal setup` to install Docker if needed, build and push the image, and start the app.
5. Choose an image registry; Docker Hub is the default, with local, AWS ECR, and GCP Artifact Registry options also described.
6. Configure secret fetching with a supported provider and keep `.kamal/secrets` out of version control.

Verdict

Pick Kamal if you are comfortable with Linux or Docker and want to deploy containerized apps to bare metal or cloud VMs. It includes rolling deployment controls, rollback, and automation hooks at no software charge. A fully managed service may suit you better if the underlying server and container concepts are difficult to use.