Get Started with Ruby on Scalingo

Installing the tools

This tutorial is depicting how to deploy a Ruby application on Scalingo

To be able to follow this tutorial, we assume that you have:

Bootstrap your project

Let’s start by creating a new Ruby application:

$ mkdir my-ruby-app
$ cd my-ruby-app

And create your Gemfile

$ bundle init

This will create a file name Gemfile. This file will be used for describing gem dependencies for your Ruby application.

Create your Ruby application

Let’s start by adding the sinatra gem to our Gemfile by adding the following line at the end of the file:

gem 'sinatra', '~> 2.0', '>= 2.0.1'

And start the gem installation:

$ bundle install

Once installed, create a file name app.rb with the following content:

require 'sinatra'

get '/' do
  'Hello World'
end

This will create a HTTP server using the Sinatra framework which will respond Hello World when asked for the / endpoint.

To run your application, use:

$ ruby app.rb

And open a browser to localhost:4567.

Using a custom port

There is one issue with that code, it is that the application will always listen to the 4567 port. But when deploying on Scalingo, the port that you should listen to is defined in the PORT environment variable. We should adapt our code to use this environment variable:

require 'sinatra'

set :port, ENV['PORT'] || 4567

get '/' do
  'Hello World'
end

This line will tell Sinatra to listen to the port 4567 or the port defined in the PORT environment variable if the PORT environment variable is defined.

You can try this by setting the PORT environment variable while launching your app:

PORT=3000 ruby app.rb

Now your app will be available at the following address: localhost:3000.

Tell Scalingo how to start your application

The last step before the deployment is to tell Scalingo how to start your application. This is done using a special file called Procfile.

Tell Scalingo to start the web process with the ruby app.rb command by creating a file called Procfile with the following content:

web: ruby app.rb

Commit your change

It’s now time to commit our changes:

$ git init
$ git add .
$ git commit -m "Initial commit"

Create the app on Scalingo

Time to deploy our app! First we need to create our app on Scalingo. We can use the CLI with the following syntax:

$ scalingo create my-ruby-app

Deploy on Scalingo

Now all the hard work is done, push your application to Scalingo and let the magic happen:

$ git push scalingo master

       Fetching source code
-----> Compiling Ruby/Rack
# [...]
-----> Procfile declares types -> web

-----> Build complete, uploading deployment cache.
 Build complete, shipping your container...
 Waiting for your application to boot...
 <-- https://my-ruby-app.osc-fr1.scalingo.io -->

Database migrations

To run a migration, you need to use a post-deployment hook.

The Ruby application starts up before the schema has changed, but does not receive a query.

As a result, if operations are started before the migration has been executed, the application may load the schema pre-migration. A restart could be necessary after the migration.

The best practice is to perform non-destructive migrations, where a column rename is performed in several steps, rather than an ALTER TABLE renaming a column.

A good example in strong_migrations gem documentation.

Where to go next

You know how to deploy a Ruby app, now develop your project and build something amazing!

Here are some links that you could find useful:

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Get Started with Ruby on Scalingo

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