The C10k problem is a limitation that most web servers currently have, which limits the web server to being able to handle a maximum of about ten thousand simultaneous connections. This limitation is due to a combination of operating system constraints and web server software limitations.

A few web servers have been developed to counter the C10K problem:

• nginx, which relies on an event-driven (asynchronous) architecture, instead of threads, to handle requests (WordPress.com uses nginx to solve the C10K problem)
• Lighttpd, which relies on an asynchronous architecture to handle requests
• Cherokee, a lightweight web server
• Tornado, a non-blocking web server and web application framework
• Deft, asynchronous, non-blocking web server running on the JVM
• Node.js, asynchronous, non-blocking web server running on Google's V8 JavaScript engine

• C10k_problem, http://www.kegel.com/c10k.html