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So I have an Amazon EC2 small instance setup on Ubuntu with Ruby Enterprise Edition running on Passenger + Nginx. I set 25 Passenger instances and performance is dropping very quickly relative to the number of concurrent connections.

For example, at 1 concurrent connection from JMeter, the response time is less than 1 second. Then at 5 concurrent connections, the response time jumps over 1 second. By the time I'm trying 10 concurrent connections the response time is averaging between 3-7 seconds!!

I imagined since I have 25 instances running, it should at least be able to handle 25 concurrent connections without much performance degradation? Obviously I'm a newbie to Web servers and all... Can someone explain to me the cause of this performance degradation?

Is it... that CPU is too slow? I feel like 1.7GB of memory should be plenty... Considering each instance apparently is running only about 30MB of memory.

Any further insights into how to configure Passenger + Nginx correctly would be greatly appreciated!!

Thanks!

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Performance degradation is normal case for any server but with 25 concurrent users seems something wrong with your server because 25 users can't generate even 1 request per second. If you were using Apache I would recommend Varnish caching server but Nginx has it's built-in cache option. I can recommend:

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