Unicorn vs. Puma vs. Passenger: which app server is right for you?

Updated version of an article first published on February 10th, 2017.The Ruby app server ecosystem has consolidated around three app servers: Unicorn, Puma, and Passenger 5. What specific problems must an app server solve for Ruby? How do you pick the right app server? Is there a need for each of these app servers in 2019?In this post I'll cover all of the above, as well as compare and contrast the three leading Ruby app servers.