Passenger vs. Unicorn
TL;DR - Use Unicorn unless you need to run multiple applications on the same host, such as testing environments or shared CMS instances. Unicorn and Passenger fundamentally differ in how they operate. There are a few similarities, however. Both have a master process that can spawn workers; both fork off workers from the master process; and both run Rack-based applications in addition to supporting older rails versions. What follows is a summary of the way the two application servers work, their benefits and problems. Read the whole article here.