Issue link: https://read.uberflip.com/i/1146286
20 | Chapter 2: Rule 2: Use a Content Delivery Network Smaller and noncommercial web sites might not be able to afford the cost of these CDN services. There are several free CDN services available. Globule (http://www. globule.org) is an Apache module developed at Vrije Universiteit in Amsterdam. CoDeeN (http://codeen.cs.princeton.edu) was built at Princeton University on top of PlanetLab. CoralCDN (http://www.coralcdn.org) is run out of New York University. They are deployed in different ways. Some require that end users configure their browsers to use a proxy. Others require developers to change the URL of their com- ponents to use a different hostname. Be wary of any that use HTTP redirects to point users to a local server, as this slows down web pages (see Chapter 11). In addition to improved response times, CDNs bring other benefits. Their services include backups, extended storage capacity, and caching. A CDN can also help absorb spikes in traffic, for example, during times of peak weather or financial news, or during popular sporting or entertainment events. One drawback to relying on a CDN is that your response times can be affected by traffic from other web sites, possibly even those of your competitors. A CDN service provider typically shares its web servers across all its clients. Another drawback is the occasional inconvenience of not having direct control of the content servers. For example, modifying HTTP response headers must be done through the service provider rather than directly by your ops team. Finally, if your CDN service pro- vider's performance degrades, so does yours. In Table 2-1, you can see that eBay and MySpace each use two CDN service providers, a smart move if you want to hedge your bets. CDNs are used to deliver static content, such as images, scripts, stylesheets, and Flash. Serving dynamic HTML pages involves specialized hosting requirements: database connections, state management, authentication, hardware and OS optimizations, etc. These complexities are beyond what a CDN provides. Static files, on the other hand, are easy to host and have few dependencies. That is why a CDN is easily leveraged to improve the response times for a geographically dispersed user population. The Savings The two online examples discussed in this section demonstrate the response time improvements gained from using a CDN. Both examples include the same test com- ponents: five scripts, one stylesheet, and eight images. In the first example, these components are hosted on the Akamai Technologies CDN. In the second example, they are hosted on a single web server. CDN http://stevesouders.com/hpws/ex-cdn.php No CDN http://stevesouders.com/hpws/ex-nocdn.php