Use PORT environment variable in Rack/Sinatra

Question

I'm looking to set the listening port within my Rack and Sinatra app, using the PORT environment variable if set otherwise to a default.

I thought I may be able to do something like the following but I'm unsure if this is even the right approach.

class ApplicationController < Sinatra::Base
  set :port, ENV['PORT'] || 3000

  get '/' do
    'Hello, World!'
  end
end

This doesn't seem to work, at least not with the rackup command. What's the correct way to do this?

Answer 1

rackup takes -p PORT argument.

You can do:

rackup -p $PORT

In config.ru you can also define the options in a comment on the first line:

#\ -p 9090

I'm not sure if that can handle $PORT.

If you look at the source code for rackup, it's very simple:

#!/usr/bin/env ruby
# frozen_string_literal: true

require "rack"
Rack::Server.start

That's the whole file.

Rack::Server.start accepts an options hash as parameter and one of the options is :Port.

You could make your own start.sh that says:

#!/usr/bin/env ruby
# frozen_string_literal: true

require "rack"
Rack::Server.start(Port: ENV['PORT'] || 3000)