Kamal Has a Free Zero-Downtime Deployment Tool — Here's How to Use It

#devops #rails #docker #deployment

Kubernetes is overkill for most apps. Capistrano is outdated. Kamal (from 37signals/Basecamp) deploys Docker containers to any server with zero downtime — no orchestrator needed.

What Is Kamal?

Kamal deploys your containerized app to bare metal servers using Docker. It handles zero-downtime deploys, rolling restarts, SSL, and multi-server setups — without Kubernetes.

Quick Start

gem install kamal
kamal init

# config/deploy.yml
service: my-app
image: my-docker-user/my-app

servers:
  web:
    hosts:
      - 1.2.3.4
      - 5.6.7.8
  worker:
    hosts:
      - 9.10.11.12
    cmd: bin/jobs

registry:
  username: my-docker-user
  password:
    - KAMAL_REGISTRY_PASSWORD

env:
  clear:
    DATABASE_URL: postgres://db.example.com/myapp
  secret:
    - RAILS_MASTER_KEY
    - STRIPE_SECRET_KEY

traefik:
  options:
    publish:
      - "443:443"
    volume:
      - "/letsencrypt:/letsencrypt"

kamal setup    # First deploy — installs Docker, Traefik, deploys app
kamal deploy   # Subsequent deploys — zero downtime

How Zero-Downtime Works

Build new Docker image
Push to registry
Pull on servers
Start new container
Health check passes
Traefik routes traffic to new container
Stop old container

No dropped requests. No maintenance windows.

Key Commands

kamal deploy          # Deploy latest version
kamal rollback        # Rollback to previous version
kamal app logs        # View application logs
kamal app exec 'bash' # SSH into container
kamal env push        # Update environment variables
kamal traefik reboot  # Restart the proxy
kamal audit           # View deployment audit log

Why Kamal

Feature	Kamal	Kubernetes	Capistrano
Complexity	Low	Very high	Medium
Zero downtime	Yes	Yes	Plugin
Multi-server	Yes	Yes	Yes
SSL	Automatic	Manual/Cert-Manager	Manual
Learning curve	1 day	Months	1 week
Cost overhead	$0	Control plane cost	$0

Who Uses Kamal

37signals — Basecamp, HEY, ONCE
Any Docker app — Rails, Node.js, Go, Python

Get Started

Deploying data pipelines? My Apify actors handle deployment automatically. Custom solutions: spinov001@gmail.com

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