A side project I’m currently working on requires the setting up and testing of many subdomains. Since the project itself is quite light, I’ve chosen to build it in the superb Sinatra. When testing Sinatra apps locally, the usual address to test in browser is 0.0.0.0:4567. While this is good enough for single domain projects, it’s a problem when you need to set up and test a project across multiple subdomains.

##Using hosts file

If you have a small number of URLs to test, adding them to your hosts file might be an option. The following format can be used in your hosts file:

127.0.0.1	one.yourapp.dev
127.0.0.1	two.yourapp.dev
127.0.0.1	three.yourapp.dev

You can then access these (assuming your app is running on port 4567) by visiting one.yourapp.dev:4567 and see it running locally.

Alternatively, if you want to be able to test against a large range of subdomains, a fun alternative is to use POW!!

##POW!!

Pow!! is a handy wrapper for running and testing multiple apps on local “.dev” URLs. It’s trivial to set up and fires up a server for you to save a few seconds each time. Installing is as easy as:

curl get.pow.cx | sh

Then setting up a symlink to your project:

cd ~/.pow
ln -s /path/to/myapp myapp

*Note: The docs seem to leave out the second “myapp” above when creating the symlink. This worked for me.

Restarting the server involves creating a text file in a tmp directory in your project, called restart.txt:

touch tmp/restart.txt

If you want the application to restart every time you refresh, create a text file called always_restart.txt:

touch tmp/always_restart.txt

Pow!! has more documentation here should you need it, but you should now be able to visit anything.myapp.dev and access your app.

Now that you have the app running at subdomains, it’s time get Sinatra to sing along.

##Sinatra Subdomain

Enter Sinatra Subdomain, a handy gem from Brazil’s @fnando. The gem is well documented and easy to set up.

Installing the Sinatra Subdomain gem:

sudo gem install sinatra-subdomain

You’ll then want to require the gem in your app:

require "sinatra/subdomain"

The gem can then be used to target specific subdomains, or take a wildcard approach. If you’re specifying your subdomains, the following will respond to the subdomain foo:

subdomain :foo do
  get '/' do
    "What does #{subdomain} rhyme with? Oh, you!"
  end
end

In my case, I found it more useful to allow any subdomains and set up routes for them as a group:

subdomain do
  # Route for the root
  get '/' do
    "You're on the #{subdomain} home page! Good job!"
  end
  # Route for a different page
  get '/bananas'
    "You're #{subdomain} for bananas! Good job!"
  end
end

While this works well for crazy.myapp.dev and mad.myapp.dev/bananas, the above won’t work for myapp.dev without the subdomain. To catch this, add the following after the subdomain section:

get '/' do
  "Now that's more like it."
end

You’ll now be set up to start putting together the logic for handling one, two or many subdomains. Good luck!