DEV Community

Alex Spinov
Alex Spinov

Posted on

Kamal 2 Has a Free API: Deploy Web Apps to Any Server Without Kubernetes

#devops #ruby #docker #tutorial

What is Kamal?

Kamal (formerly MRSK) is a deployment tool from the creators of Rails (37signals/Basecamp). It deploys containerized web apps to any server — bare metal, VPS, or cloud — without Kubernetes complexity.

Kamal 2 powers HEY.com and Basecamp in production.

Quick Start 

gem install kamal
kamal init
kamal setup
kamal deploy
Enter fullscreen mode Exit fullscreen mode

Configuration 

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

servers:
  web:
    hosts:
      - 192.168.1.1
      - 192.168.1.2
    options:
      memory: 512m
  worker:
    hosts:
      - 192.168.1.3
    cmd: bundle exec sidekiq

registry:
  username: myorg
  password:
    - KAMAL_REGISTRY_PASSWORD

env:
  clear:
    RAILS_ENV: production
    DATABASE_URL: postgres://db-host/myapp
  secret:
    - RAILS_MASTER_KEY
    - STRIPE_SECRET_KEY

proxy:
  ssl: true
  host: myapp.com
  app_port: 3000

accessories:
  db:
    image: postgres:16
    host: 192.168.1.4
    port: 5432
    env:
      clear:
        POSTGRES_DB: myapp_production
      secret:
        - POSTGRES_PASSWORD
    directories:
      - data:/var/lib/postgresql/data
  redis:
    image: redis:7
    host: 192.168.1.4
    port: 6379
    directories:
      - data:/data
Enter fullscreen mode Exit fullscreen mode

Zero-Downtime Deploys 

# Deploy with zero downtime
kamal deploy

# What happens:
# 1. Build Docker image locally
# 2. Push to registry
# 3. Pull on servers
# 4. Start new container
# 5. Health check passes
# 6. Switch traffic (kamal-proxy)
# 7. Stop old container
Enter fullscreen mode Exit fullscreen mode

The built-in kamal-proxy handles traffic switching — no nginx config needed.

Key Commands 

# First-time setup (installs Docker, kamal-proxy)
kamal setup

# Deploy latest code
kamal deploy

# Rollback to previous version
kamal rollback

# View logs
kamal app logs
kamal app logs -f  # Follow

# Run console
kamal app exec -i 'bin/rails console'

# Run one-off task
kamal app exec 'bin/rails db:migrate'

# Manage accessories
kamal accessory boot db
kamal accessory logs db

# Check server details
kamal details
Enter fullscreen mode Exit fullscreen mode

Kamal 2 New Features

Built-in Proxy (replaces Traefik)

Kamal 2 ships with kamal-proxy — a purpose-built reverse proxy:

proxy:
  ssl: true
  host: myapp.com
  buffering:
    requests: true
    responses: true
    max_request_body: 10m
  response_timeout: 30
  healthcheck:
    interval: 3
    path: /up
    timeout: 3
Enter fullscreen mode Exit fullscreen mode

Aliases 

# config/deploy.yml
aliases:
  console: app exec -i 'bin/rails console'
  logs: app logs -f
  shell: app exec -i bash
Enter fullscreen mode Exit fullscreen mode 
kamal console  # Opens Rails console on production
kamal logs     # Follows production logs
Enter fullscreen mode Exit fullscreen mode

Multi-App on Single Server 

# app1/config/deploy.yml
proxy:
  host: app1.com

# app2/config/deploy.yml  
proxy:
  host: app2.com
Enter fullscreen mode Exit fullscreen mode

Multiple apps share the same server, kamal-proxy routes by hostname.

Cost Comparison

Setup Monthly Cost
Heroku (2 dynos) $50-100
AWS ECS/Fargate $50-150
Kubernetes (EKS) $75-200+
Kamal + Hetzner VPS $5-20

Kamal + a $5 VPS = production-ready deployment.

Need help deploying apps or setting up CI/CD pipelines?

📧 spinov001@gmail.com
🔧 My tools on Apify Store

Kamal, Docker Compose, or Kubernetes? Share your deployment stack!

Top comments (0)