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I intermittently perform 3rd party speed tests using on my server. Recently, I have started to see long yellow bars for some of the static content on my sites, like images and CSS files (my understanding is yellow bars measure the amount of time from the request being made to the serving responding with "connect"). Checking my historical test results, I confirmed that there were never issues with to-connect times in the past, and that they only started after a few new websites were added to my server. Hence I'm thinking that the delay is being caused by a capacity limit of some kind set in my nginx.conf.

How should I move forward to further diagnose - and address - this issue?

OS is Centos, NGINX is built from source, 1.0.5.

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You'll need to know far more about the cause of the delays. The problem could be network packet loss (if your new sites are generating enough traffic to hit a limit of some sort in your infrastructure) or your server could be running overloaded.

To diagnose the problem further, you'll need to know what exactly your monitoring system is seeing (which is why I don't like third-party monitoring; you can only dig as deep as they'll let you), and then use that as the basis for further investigation. If you're not already collecting comprehensive performance statistics on your systems, now would be an awfully good time to start.

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I am already collecting performance stats on my system via Munin - would that be considered a comprehensive enough system? It's setup to monitor NGINX requests + NGINX status, through the nginx stub_status module I believe - – Professor Frink Aug 8 '11 at 13:19
What charts should I be looking at? I can post links to any of Munin's charts here if that would help - – Professor Frink Aug 8 '11 at 13:29

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