We removed our free Sandbox April 25th.
You can read more on our blog.


Today we’re going to go through a demo application that will show you a very simple example of running a Sinatra and Twilio application on dotCloud! Twilio provides a REST API for adding telephony to your apps. Using Twilio you can easily add voice and SMS capabilities to your application! While this tutorial uses Ruby, Twilio is simple to use in every language they support (PHP, ColdFusion, Ruby, Python, C#, and more). You can read all about Twilio on the Twilio homepage.

The sources of this tutorial are available on GitHub: https://github.com/caleywoods/cloudsinger.

dotCloud Build File

The dotCloud Build File, dotcloud.yml describes our stack.

We declare a single Ruby service. We use Ruby because it features two useful things for us:

  • a Ruby interpreter and a mechanism to install gems;
  • a public-facing HTTP server (Nginx).

The role and syntax of the dotCloud Build File is explained in further detail in the documentation,


  type: ruby

YAML Configuration File

Next we’re adding a YAML file that contains our Twilio information that will be used later in app.rb. If you don’t have an account already you can sign up for one on the Twilio homepage.


If you don’t have any “Twilio number” yet, you can use the one of e.g. your cellphone or landline. On your Twilio dashboard, go to “Numbers”, then “Verified Numbers”, and enter your phone number. Twilio will call this number to make sure that it’s your number.

However, if you are using a free account, the “Twilio number” must be the one of the sandbox, i.e. 4155992671 as we write this document.

Change the settings in this file to match your Twilio number, SID, and token. app.rb is already setup to use the settings you place in config.yml.


caller_id: "your_twilio_number"
twilio_sid: "your_twilio_sid"
twilio_tkn: "your_twilio_token"

Demo Sinatra Application and Rack Config

This is a simple Sinatra application and rack configuration file. The Sinatra application is contained in app.rb and is fairly straightforward. This application will display a simple form that asks for a phone number and gives a textarea for the message you wish to send via SMS.

config.ru is also telling rack to serve static files from public/css and public/images. Sinatra, by default, looks in public (and we’ve told it again by saying :root => 'public') so you won’t need to use it when referring to static file locations within your Sinatra application. In this example, you would link the CSS by writing /css/style.css; see how we didn’t use public/ at the beginning of the path? You can find more information on the config.ru file at this site.

You should have an account by now and you should’ve configured your phone number, SID, and Twilio token in config/config.yml. As a bonus, twilio gives you $30 when you sign up!!

Our application isn’t quite ready yet, but almost. I’ve chosen to use Haml for templates, so we’ll add those views shortly.


require 'sinatra'
require 'yaml'
require 'twilio'

config = YAML.load_file('./config/config.yml')
CALLER_ID = config['caller_id']

get '/' do
  haml :index

post '/sms' do
  Twilio.connect(config['twilio_sid'], config['twilio_tkn'])
  number  = params[:number]
  message = params[:msg]

  Twilio::Sms.message(CALLER_ID, number, message)

  redirect '/'


require './app'
use Rack::Static, :urls => ["/css", "/images"], :root => "public"
run Sinatra::Application

Gemfile & Dependencies

To tell dotCloud to automatically install the gems we need (Haml and Twilio), we create a standard Gemfile. dotCloud will detect this and automatically use bundler to install dependencies defined in Gemfile.

This also gets ran when you scale your application on dotCloud. See http://gembundler.com/gemfile.html for details about Bundler and the Gemfile format.


source :rubygems

gem 'sinatra'
gem 'haml'
gem 'twilio'

Views & CSS/Images

Now that we’ve gotten the Gemfile taken care of, dotCloud can install our dependencies we add in this last part of our application. We’re adding all the views used, as well as the images and CSS of the page.

This tutorial is using Haml as the markup language but you could substitute your preferred language (erb, slim, etc). Let’s talk just a bit about some of the views.

First, layout.haml serves to generate the “layout” of our site or “what goes where” if you will. Thanks to Haml we save quite a bit of typing. Sinatra by default looks for a file named layout in the views/ directory to serve as the applications layout, we don’t need to do anything special to get this to work.

The index.haml gives us the header text, image, and ‘view source’ link and tells Sinatra to render our two remaining templates, text and footer.

text.haml is the form that contains the input fields for “Number” and “Message” as well as the “Text Me!” button. Finally footer.haml is made up of just the Twitter logo. It might be overkill in this simple example to give this its own template but if the application were to grow it makes it a little easier to add things and keeps our templates small.

With these files added you can now dotcloud push and then visit the URL of your deployed app. When you visit the URL you should be able to supply a phone number and a message (140 characters or less of course!) that you would like to send. Click on “Text Me!” and if you’ve setup config.yml correctly and all systems are go, you should get a text shortly at the number you provided. Please note that if you’re using a Twilio demo account you may need to edit app.rb line 33. In this file you will need to add your Twilio PIN as the first argument to Twilio::Sms.message(), this is also documented directly in app.rb.

This is just the beginning of what’s possible with Twilio. You can make and receive phone calls, record them, create conferences, and receive SMS messages. In a non-trivial application you would login to the Twilio dashboard and setup Twilio to HTTP POST to a URL of your app when someone calls or SMS messages your application and you would then write the code to handle those POST events.

I hope you’ve enjoyed this dotCloud + Twilio demo, feel free to drop us a line if you have problems.