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The following are two graph of my digital ocean vps instance handle load test request. 10K/s, The only different is the request file size, first is 10K, the second is 20K. Can any one point out the bottle neck of my server setup?

P.S resources peak usage: CPU 20%, memory 10% Network IO 69MB/s(This may the problem lies) Disk IO 0.13% enter image description here

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DigitalOcean 8-core instance 16G RAM, using Nginx serving static 10k/20k image file.

update! I put load balancer(HAProxy) into a separate VPS(8 core), I found the cpu usage is pretty high as the 3rd gram shows(5k request on 10k image)

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The second graph shows 100.000 clients, not the 10K you mention. Also without knowing anything about your platform (is this a webserver, an MQ broker,...), the currently implemented configuration, the type of data being served (static vs. dynamic), amount of RAM, etc, it is difficult to diagnose anything. – dawud Mar 15 '14 at 15:21
@dawud thanks for your comment. I've updated the detail – mko Mar 15 '14 at 15:57
How are you caching this static content? – dawud Mar 15 '14 at 15:58
What uplink? 690Mb/s looks like a good number for a 1gigbit port. – TomTom Mar 15 '14 at 16:30
@dawud I'm using varnish before nginx as file server – mko Mar 15 '14 at 17:20

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