title: Slow server response, lots of free CPU and RAM
body: <p>I've been pulling my hair out for the last few days on this and have finally succumbed to asking for help.</p>
  
  <p>Quick run down... I've got a website that receives around 10-20K visits a day. I'm using a <a href="http://aws.amazon.com/ec2/instance-types/#instance-details" rel="nofollow">large EC2 Instance from Amazon</a> and a <a href="http://aws.amazon.com/rds/#features" rel="nofollow">small RDS instance</a>.</p>
  
  <p>I have Wordpress Multisite installed on there with a variety of plugins etc. I'm using APC and Memcache, as well as Varnish. All static content (images, JS, CSS etc) is stored on a CDN. I also have CLoudFlare sitting in front of all this.</p>
  
  <p>My problem is that despite having over 5 gig of spare RAM and the CPU never spiking above 40%, the response time of the website is really poor. Likewise, my RDS instance never peaks over 20% CPU usage.</p>
  
  <p>Unless I'm un-registered user hitting a Varnish cached page, then it loads lightning quick.</p>
  
  <p>So I'm not exactly sure what I can be doing to try and troubleshoot the problem. I've run various profilers and plugin checkers to see if any of them are causing issues in the Wordpress install and none have shown red flags.</p>
  
  <p>Could it be my Apache settings? PHP settings? Something else? I'm basically asking for this I can check/change/monitor to try and debug this problem. It's really frustrating.</p>
  
  <p>Thanks in advance and if you need/want any more info, just let me know.</p>