Ruby Sinatra Webservice running on localhost:4567 but not on IP

Following worked for me.

ruby app.rb -o 0.0.0.0

When using the built-in server through the run! if app_file == $0 check, Sinatra's doc explains that set :bind, '0.0.0.0' is required to make the interface available outside the localhost layer.

It is not required to use a custom IP address or a reverse DNS (mydomain.com…): '0.0.0.0' is the legit value expected by Sinatra, which will be interpreted correctly.

Therefore, a minimal, self-contained Sinatra application made available on all interfaces, not only localhost, would be:

require 'sinatra/base'

class MyApp < Sinatra::Base
  set :bind, '0.0.0.0'

  get '/' do
    'Hello World'
  end

  run! if app_file == $0
end

To set server hostname or IP-address use sinatra setting bind like

set :bind, '192.168.103.99'