Chapter 4. Rule 2: Use a Content Delivery Network

The average user's bandwidth increases every year, but a user's proximity to your web server still has an impact on a page's response time. Web startups often have all their servers in one location. If they survive the startup phase and build a larger audience, these companies face the reality that a single server location is no longer sufficient—it's necessary to deploy content across multiple, geographically dispersed servers.

As a first step to implementing geographically dispersed content, don't attempt to redesign your web application to work in a distributed architecture. Depending on the application, a redesign could include daunting tasks such as synchronizing session state and replicating database transactions across server locations. Attempts to reduce the distance between users and your content could be delayed by, or never pass, this redesign step.

The correct first step is found by recalling the Performance Golden Rule, described in Chapter 1:

Only 10–20% of the end user response time is spent downloading the HTML document. The other 80–90% is spent downloading all the components in the page.

If the application web servers are closer to the user, the response time of one HTTP request is improved. On the other hand, if the component web servers are closer to the user, the response times of many HTTP requests are improved. Rather than starting with the difficult task of redesigning your application in order to disperse the application web servers, it's better to first disperse the component web servers. This not only achieves a bigger reduction in response times, it's also easier thanks to content delivery networks.