Deploying Rails application with Kamal and Postgres

2 minute read

This article assumes the file exists with sqlite config:

For complete config visit Kamal Config Generator

Pro Tip:

Run the following command to switch the database from sqlite to PostgreSQL:

rails db:system:change --to=postgresql

Verify the changes and then you can jump to step 4.

1. Gemfile

First, update the Gemfile to use pg as the database for Active Record.

-# Use sqlite3 as the database for Active Record
-gem "sqlite3", ">= 2.1"
+# Use pg as the database for Active Record
+gem "pg", "~> 1.1"

2. Dockerfile

Next, update the Dockerfile to install the postgresql-client and libpq-dev packages.

 # Install base packages
 RUN apt-get update -qq && \
-    apt-get install --no-install-recommends -y curl libjemalloc2 libvips sqlite3 && \
+    apt-get install --no-install-recommends -y curl libjemalloc2 libvips postgresql-client && \
     rm -rf /var/lib/apt/lists /var/cache/apt/archives


 # Install packages needed to build gems
 RUN apt-get update -qq && \
-    apt-get install --no-install-recommends -y build-essential git pkg-config && \
+    apt-get install --no-install-recommends -y build-essential git libpq-dev pkg-config && \
     rm -rf /var/lib/apt/lists /var/cache/apt/archives

3. config/database.yml

Update the config/database.yml to use postgres as the adapter.

Note: Make sure to replace the host to <%= ENV["DB_HOST"] %> and password in production block to <%= ENV["POSTGRES_PASSWORD"] %>

default: &default
  adapter: postgresql
  encoding: unicode
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>

development:
  <<: *default
  database: kamal_demo_development

test:
  <<: *default
  database: kamal_demo_test

production:
  primary: &primary_production
    <<: *default
    host: <%= ENV["DB_HOST"] %>
    database: kamal_demo_production
    username: kamal_demo
    password: <%= ENV["POSTGRES_PASSWORD"] %>
  cache:
    <<: *primary_production
    database: kamal_demo_production_cache
    migrations_paths: db/cache_migrate
  queue:
    <<: *primary_production
    database: kamal_demo_production_queue
    migrations_paths: db/queue_migrate
  cable:
    <<: *primary_production
    database: kamal_demo_production_cable
    migrations_paths: db/cable_migrate

4. config/deploy.yml

Update the config/deploy.yml to add environment variables the db accessory.

<% require "dotenv"; Dotenv.load(".env") %>

service: kamal-demo
image: yourregistryusername/kamal-demo
servers:
  web:
    - 12.34.56.78

proxy:
  ssl: true
  host: example.com

registry:
  username: yourregistryusername
  password:
    - KAMAL_REGISTRY_PASSWORD

env:
  secret:
    - RAILS_MASTER_KEY
    - POSTGRES_PASSWORD
  clear:
    DB_HOST: kamal-demo-db
    POSTGRES_USER: kamal_demo
    POSTGRES_DB: kamal_demo_production
    SOLID_QUEUE_IN_PUMA: true

volumes:
  - 'kamal_demo_storage:/rails/storage'

asset_path: /rails/public/assets

builder:
  arch: amd64

accessories:
  db:
    image: postgres:16
    host: 12.34.56.78
    port: 5432
    env:
      clear:
        DB_HOST: kamal-demo-db
        POSTGRES_USER: kamal_demo
        POSTGRES_DB: kamal_demo_production
      secret:
        - POSTGRES_PASSWORD
    files:
      - db/production.sql:/docker-entrypoint-initdb.d/setup.sql
    directories:
      - data:/var/lib/postgresql/data

5. .env

Add the POSTGRES_PASSWORD to the .env file.

KAMAL_REGISTRY_PASSWORD=dckr_pat_*******************o
POSTGRES_PASSWORD=postgres_*******************_password

6. .kamal/secrets

Add the POSTGRES_PASSWORD to the .kamal/secrets file.

KAMAL_REGISTRY_PASSWORD=$KAMAL_REGISTRY_PASSWORD
POSTGRES_PASSWORD=$POSTGRES_PASSWORD

RAILS_MASTER_KEY=$(cat config/master.key)

7. Deploy

Once done you should be able to deploy your Rails application with Kamal.

kamal deploy

If you get an error saying the service app-name-db already exists you can remove the service using the following command and then re-deploy.:

kamal accessory remove db
kamal deploy

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