Kamal Rails on Hetzner Series Part 2: Deploy Postgres with your Rails application

In Part 1 of this Kamal series, we deployed a vanilla Rails application to a remote server using Kamal. By default, Rails applications use SQLite, but most production applications require Postgres. This article shows how to configure Postgres and deploy it on the same server as your Rails application using Kamal.

This article assumes you have a Rails application backed by Postgres running locally. If you use a different database like MySQL, you can adapt these instructions accordingly. If you’re using SQLite, you can skip this article.

There are two approaches to deploying Postgres with a Rails application:

1. On the same VM as your application
2. Using a managed database service

This article covers the first approach—deploying Postgres on the same server as your Rails application. For a managed database service, see the AWS RDS article.

Step 1: Configure the Database in deploy.yml

• Add database configuration under the accessories section of your config/deploy.yml
• Your config/deploy.yml should look like:

# config/deploy.yml file

# Inject ENV variables into containers (secrets come from .env).
# Remember to run `kamal env push` after making changes!
env:
  clear:
    DB_HOST: <ipv4_address_of_your_server>
    RAILS_SERVE_STATIC_FILES: true
    RAILS_LOG_TO_STDOUT: true
  secret:
    - RAILS_MASTER_KEY
    - POSTGRES_PASSWORD

accessories:  
  db:
    image: postgres:15
    host: <ipv4_address_of_your_server>
    port: 5432
    env:
      clear:
        POSTGRES_USER: 'kamal_app_demo'
        POSTGRES_DB: 'kamal_app_demo_production'
      secret:
        - POSTGRES_PASSWORD
    directories:
      - data:/var/lib/postgresql/data

Step 2: Configure Environment Variables

• Add POSTGRES_PASSWORD to your .env file:

# .env file
KAMAL_REGISTRY_PASSWORD=<docker_password>
RAILS_MASTER_KEY=<master_key_of_production_environment>
POSTGRES_PASSWORD=<secure_password>

• Choose a strong password for POSTGRES_PASSWORD and keep it secure. Never commit this file to version control.

Step 3: Update database.yml

• Update your config/database.yml to use environment variables:

# config/database.yml
production:
  <<: *default
  host: <%= ENV["DB_HOST"] %>
  username: <%= ENV["POSTGRES_USER"] %>
  database: <%= ENV["POSTGRES_DB"] %>
  password: <%= ENV["POSTGRES_PASSWORD"] %>

Step 4: Deploy Your Application

After completing the configuration above, deploy to your remote server:

kamal env push
kamal accessory boot db
kamal deploy

To reset the server and deploy with the new Postgres configuration:

kamal remove
kamal setup

Important Notes

• This configuration deploys Postgres on the same machine as your Rails application
• For advanced setups with Postgres on a separate machine or other complex requirements, refer to the AWS RDS article

Next Part: Enable HTTPS

So far, we’ve accessed the server using HTTP. In Part 3 of this Hetzner series, we’ll configure HTTPS and SSL certificates.

Continue to Part 3: Enable HTTPS

Previous articles in this Hetzner series:

• Part 1: Deploy Rails application on Hetzner

NOTE:

• If this article is out of date, please don’t hesitate to contact me on Twitter from this page and I’ll be happy to update it.
• Listen to this podcast where DHH talks about Rails and Kamal.
• If you would like to search for specific terms or concepts or names in Ruby/Rails podcasts, check out rubypodcatcher.com