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Alex Spinov
Alex Spinov

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

#kamal #docker #deployment #devops

Kamal (by 37signals/Basecamp) deploys Docker containers to bare metal servers with zero-downtime. No Kubernetes, no PaaS — just SSH and Docker. It's how HEY and Basecamp deploy.

Why Kamal?

  • No Kubernetes — deploy to any Linux server via SSH
  • Zero downtime — rolling deploys with health checks
  • Multi-server — deploy to multiple servers at once
  • Traefik built-in — automatic SSL and routing
  • Free — open source, works with any $5 VPS

Install 

gem install kamal

# Or in your project
bundle add kamal
kamal init
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Configuration 

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

servers:
  web:
    - 192.168.1.1
    - 192.168.1.2
  workers:
    hosts:
      - 192.168.1.3
    cmd: bundle exec sidekiq

registry:
  username: my-user
  password:
    - KAMAL_REGISTRY_PASSWORD

env:
  clear:
    RAILS_ENV: production
    DATABASE_URL: postgres://...
  secret:
    - RAILS_MASTER_KEY
    - STRIPE_SECRET_KEY

traefik:
  options:
    publish:
      - "443:443"
    volume:
      - "/letsencrypt:/letsencrypt"
  args:
    entryPoints.websecure.address: ":443"
    certificatesResolvers.letsencrypt.acme.email: "admin@example.com"
    certificatesResolvers.letsencrypt.acme.storage: "/letsencrypt/acme.json"
    certificatesResolvers.letsencrypt.acme.httpChallenge.entryPoint: web

healthcheck:
  path: /healthz
  port: 3000
  interval: 10s
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Commands 

# First deploy (sets up Docker, Traefik, everything)
kamal setup

# Deploy new version
kamal deploy

# Rollback
kamal rollback

# App logs
kamal app logs

# Remote console
kamal app exec -i bash
kamal app exec -i 'rails console'

# Run one-off commands
kamal app exec 'rails db:migrate'

# Check status
kamal details

# Manage environment
kamal env push

# Manage accessories (databases, redis)
kamal accessory boot all
kamal accessory logs redis
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Accessories (Databases, Redis) 

# config/deploy.yml
accessories:
  db:
    image: postgres:16
    host: 192.168.1.1
    port: 5432
    env:
      clear:
        POSTGRES_DB: myapp_production
      secret:
        - POSTGRES_PASSWORD
    directories:
      - data:/var/lib/postgresql/data

  redis:
    image: redis:7
    host: 192.168.1.1
    port: 6379
    directories:
      - data:/data
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Kamal vs Alternatives

Kamal Kubernetes Dokku Coolify
Complexity Low Very High Low Low
Multi-server Yes Yes No Yes
Zero-downtime Yes Yes Yes Yes
GUI No (CLI) Dashboard Web UI Web UI
Cost $0 + VPS $0 + VPS $0 + VPS $0 + VPS

Resources

Need deployment or DevOps tools? Check my Apify actors or email spinov001@gmail.com.

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