Gaurav Varma

In Feb 2023, Basecamp released Kamal (formerly MRSK) — a deployment tool designed to make zero-downtime deploys simple, fast, and infrastructure-independent.

Kamal is opinionated, Docker-based, and avoids cloud-specific lock-in by relying on SSH and Docker Compose. It’s a modern replacement for tools like Capistrano and Heroku pipelines for self-hosted Rails apps.

What is Kamal?

Kamal is an open-source deployment tool created by @dhh, inspired by the simplicity of Heroku but designed for self-hosted environments. It focuses on:

Zero-downtime deployments
Simple configuration
Docker-first approach
No vendor lock-in
Fast rollback

Kamal deploys your Rails app as a set of containers across one or more remote servers using SSH, Docker, and Docker Compose.

How does Kamal work?

Here’s the basic flow:

You define your app and servers in a deploy.yml file.
Kamal builds a Docker image locally or remotely.
It pushes the image to your servers.
Kamal performs a rolling update using Docker containers.
Nginx or Traefik handles traffic routing with zero downtime.

1kamal init
2# Creates config/deploy.yml
3
4kamal deploy
5# Deploys your app across all defined servers

You can also rollback instantly:

1kamal rollback

Key Features

✅ Zero-downtime deploys with rolling restarts
✅ Docker-native with simple container orchestration
✅ Configurable load balancing (Nginx, Traefik, HAProxy)
✅ Integrated asset building
✅ Built-in health checks
✅ Environment parity with production

Why Kamal?

For years, Capistrano and cloud PaaS platforms (Heroku, Render) have dominated Rails deployments. Kamal offers:

More control than Heroku
Less complexity than Kubernetes
Better developer experience than Capistrano
Complete Docker parity with local and prod

It’s great for teams who want to:

Host Rails apps on their own servers
Avoid cloud lock-in
Deploy in edge or hybrid environments

Real-World Setup Example

Your deploy.yml might look like this:

1service: myapp
2image: myregistry.com/myapp
3servers:
4  web:
5    hosts:
6      - 192.168.0.2
7      - 192.168.0.3
8env:
9  secret_key_base: <%= ENV["SECRET_KEY_BASE"] %>

Kamal handles the build, push, and deployment process for you — all without touching AWS CLI, Terraform, or Kubernetes.

Summary

Kamal is a bold step forward in Rails deployment simplicity. If you’ve ever wanted Heroku-like ease without the vendor lock-in — or you're tired of fiddling with Capistrano — Kamal is worth exploring. It makes Dockerized Rails deploys predictable, fast, and production-ready with minimal overhead.

Basecamp unveils Kamal (MRSK) for zero-downtime Rails deploys