ps -ax shows me a "rack" process. Is this normal?

I run a webpage using the Ruby web-framework Sinatra on my Ubuntu server. Today I looked to my processes and found these two lines:

30129 ?        S      0:00 Passenger ApplicationSpawner: /var/www/bla.com             开发者_如何学编程                                       
30139 ?        S      0:00 Rack: /var/www/bla.com

I never noticed these before. Are these normal, or should I be concerned?

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It should be normal. Check out what Rack is. Killing that process could risk your webpage functionality, so don't do it.

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From what I could find, Rack is used by Sinatra:

Sinatra rides on Rack, a minimal standard interface for Ruby web frameworks.

from http://www.sinatrarb.com/intro

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Yes, it's normal. Passenger is your webserver, and Rack is the middleware between your server and Sinatra framework.