Serving Web pages is easy

It's easy to be lulled into complacency with a Web server's performance. Serving a little bit of static traffic is a very lightweight operation; seeing a low load average might lead us to believe that we have plenty of capacity.

Serving Web pages is hard

The load average on a system maybe more linear when the CPU's duties are strictly confined to numeric computation. Maintaining servers for Web duties is a very different endeavor from maintaining servers for astronomy labs and graphics rendering.

Web servers are subject to bottlenecks

Of course, CPU is a just tells a fraction of the story. Web server performance is dependent on the I/O characteristics of the OS and its use of the disks, disk controllers and network interfaces.

You've done your performance optimizations but you still need more capacity. Now what?