I like puma, but I thought it was interesting that the left passenger out of their performance graphs. Seems odd to omit the most popular ruby application server from the results.
All of the servers listed here are standalone servers, while Passenger is a module for existing servers. I don't really see why you couldn't include Passenger here, but it seems like they're only comparing like to like, which I guess is fair.
You can use Passenger as a standalone server too, it's called Passenger Standalone. You can install it with 'gem install passenger', and run it by running 'passenger start'.
Oh, so you can. I actually went and checked the Passenger site to see if my information was current since I mainly use Puma these days, but I didn't scroll down far enough to see the standalone version.
But installing it as a module still seems to be the recommended method, so I can see still see why it isn't included in a list of servers that are meant to be proxied to.
