To expand on this: You have to remove the port declaration from the line for Unicorn in your Procfile, and then add a line like this to your unicorn.rb file to

To expand on this: You have to remove the port declaration from the line for Unicorn in your Procfile, and then add a line like this to your unicorn.rb file to define the listener port along with adjusting the backlog size: listen ENV['PORT'], :backlog => Integer(ENV['UNICORN_BACKLOG'] || 100)