You should also make sure that your CDN provider supplies the usage reporting that you need. IIS can log all requests, and software such as Microsoft Commerce Server 2000 makes building reports on IIS logs easy. However, if you use a CDN, many user requests won't ever reach your Web servers. You can still track your users' behavior, but doing so is a little more difficult with a CDN. All the major CDN providers offer reporting and log-aggregation services, but you'll need to gather your log files from your CDN provider and correlate them with your own IIS logs.
The Future of CDNs
As I mentioned earlier, the original concept behind CDNs was to push simple, static Web site content out to the edges of the Internet. However, the modern Internet is neither simple nor static. Most popular Web sites include personalized content, shopping-cart capabilities, or search features. Because traditional CDNs can't cache dynamic content, they must forward all requests for such Web pages to the Web site. In these situations, CDNs actually slow site performance by adding an unnecessary step.
Managed Edge Services, or edge computing, describes the next generation of CDNs, which are capable of dynamically generating some types of content at the edge of the Internet—without sending a request to the host Web site. Personalization features are the first dynamic content type to be pushed to the edge of the Internet.
You've probably used a personalized Web site. If you've surfed to CNN.com, the first time you did so, you were asked whether you wanted to visit the US, European, or Asian site. The site stored your answer in a cookie on your computer. Each subsequent time that you go to CNN.com, your browser sends the cookie to the site so that it can send you the correct regional version. Sending a particular page in response to a cookie is easy for a dynamic Web site but is a fairly recent advancement for CDNs.
Over the next few years, CDNs will add much more intelligence. You'll be able to browse an online catalog, purchase an item, and receive a receipt without the CDN sending your request on to the Web site. Transaction processing and database content will be on CDN nodes, and synchronization between the nodes and the Web site will happen transparently to the users and Web masters. Eventually, the need for an origin IIS server might be eliminated completely, and content authors will publish updates directly to the CDN.
Edge Side Includes (ESI) are the best-developed standards for dynamic CDN pages. For more information about ESI, visit http://www.esi.org.
Who Needs a CDN?
If you answer yes to any of these questions, you should investigate CDNs.
- Does your site have extreme seasonal peaks in traffic?
- Is your site prone to random bursts of traffic?
- Is response time currently unacceptable?
- Are you paying your ISP too much for bandwidth?
- Do you have a plan for scaling your site if your traffic increases?
For a list of CDN service providers, visit http://www.webreference.com/internet/software/site_management/cdns.html. For more general information about CDNs, visit http://www.caching.com.
CDNs aren't for everyone, but for many sites, they're a necessity. Some companies use them to improve their site's performance so that visitors will keep coming back to their Web site. The additional revenue they receive from customers more than offsets the CDN subscription. Other companies can justify a CDN because the CDN bandwidth charges are lower than those of their hosting service provider. CDNs can reduce the number of IIS servers a site needs, which offsets hardware, software, and administrative costs.
Understanding CDNs is important because they can save you some cash. More important, if your site suddenly gets busy, they can save your reputation.
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