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Ruby on Rails Docker CMD Startup Script

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#!/bin/sh

# wait for db
# ...

if bundle exec rails db:exists ; then
    echo 'Running database migrations...'
    bundle exec rails db:migrate
else
    echo 'Creating and seeding application database...'
    bundle exec rails db:create
    bundle exec rails db:migrate
    bundle exec rails db:seed
fi

# other startup commands
# ...

bundle exec rails server -b 0.0.0.0

Docker CMD startup script for a containerized Ruby on Rails project to create or migrate the project database then start the application server.

Dependencies

The script requires the custom rake task db:exists. Make sure the task is added to the project repository and copied into the container image in the Dockerfile.

Details of the rake task can be found here: Check if Ruby On Rails Database Exists Using Rake

Usage

Add Script to Repository

Add script to the project repository under a suitable directory and filename, for example: ./.docker/scripts/app-startup.sh

Ensure the script file is executable: sudo chmod +x ./.docker/scripts/app-startup.sh

Wait for Database to be Ready

Add a command at the top of the script which waits for the database to be ready. This is database specific, for example, for MySQL:

# wait for db
until mysqladmin ping -h "$DB_HOST" --silent ; do
    sleep 1
done

For PostgreSQL:

# wait for db
until pg_isready -U "$DB_USERNAME" -h "$DB_HOST" ; do
    sleep 1
done

Make sure the relevant environment variables such as DB_HOST are available in the container.

Add Additional Startup Commands

Add any additional required startup commands to the script, for example generating a sitemap using the sitemap_generator gem: bundle exec rails sitemap:refresh:no_ping

Add and Run in Dockerfile

Make sure the script file is copied into the container image in the Dockerfile.

Run the script as the default command in the Dockerfile using the CMD instruction, for example: 

CMD ["./.docker/scripts/app-startup.sh"]
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