Requirements

Before doing this tutorial you should have setup your environment:

• Setup the SSH authentication, it has to be done to let you push your application on the platform.
• Install ‘scalingo’ Command Line Interface

Initialize your application

$ crystal init app my-app
$ cd my-app

The shard.yml file declares the name of the project in his name field. This name will be used by Scalingo to determine the main source file to compile: ./src/<NAME>.cr. In this example, it will be ./src/my-app.cr.

Write a base server file

The main file of this sample application is src/my-app.cr:

require "http/server"

bind = "0.0.0.0"
port = 8080

server = HTTP::Server.new(bind, port) do |context|
  context.response.content_type = "text/plain"
  context.response << "Hello world, got #{context.request.path}"
end

puts "Listening on https://#{bind}:#{port}"
server.listen

To launch the web server type :

$ crystal src/my-app.cr

Modify it for Scalingo

Here your server listen on 0.0.0.0:8080 but Scalingo need to configure the listening port in order to deploy your app.

You must add a --port flag to set a custom listening port.

The src/my-app.cr file now looks like:

require "http/server"
require "option_parser"

bind = "0.0.0.0"
port = 8080

OptionParser.parse! do |opts|
  opts.on("-p PORT", "--port PORT", "define port to run server") do |opt|
    port = opt.to_i
  end
end

server = HTTP::Server.new(bind, port) do |context|
  context.response.content_type = "text/plain"
  context.response << "Hello world, got #{context.request.path}"
end

puts "Listening on https://#{bind}:#{port}"
server.listen

Commit your application

git init
git add .
git commit -m "Base Crystal application"

Create your application on Scalingo and deploy

Create your application

$ scalingo create my-app

Specify a custom buildpack

Crystal is not natively supported by Scalingo. To deploy a Crystal code you should use a custom buildpack.

$ scalingo --app my-app env-set BUILDPACK_URL=https://github.com/crystal-lang/heroku-buildpack-crystal.git

Send your application to Scalingo

git push scalingo master

Access your application

…
Waiting for your application to boot...
<-- https://my-app.osc-fr1.scalingo.io -->

Live demo

This application is currently running on Scalingo here.