Much is made about the power that a Content Delivery Network (CDN) can add to multi-media websites. The CDN's caching technology brings the content closer to the user, decreasing download times and greatly reducing the load placed on the origin server. Many people and businesses benefit from CDNs in monstrous ways; however, there are times where a CDN may not be the best solution for a given situation. Any online business would do well to ask the question: is a CDN the right choice for me?
In the beginning, the Internet didn't have a lot of bandwidth to go around. Content Delivery Networks were invented to bring large amounts of content to users and circumvent the limitations of the Internet, allowing more data to be transferred using less space. With the way the Internet has expanded over the last several years, the value of Content Delivery Networks has increased dramatically.
When evaluating your company's need for a Content Delivery Network, there are several CDN business models to consider:
- Customer origin model. Using this model, the client retains content on a storage server inside their own internal network. In terms of the CDN, the origin server is still contained inside the client network. This gives the client total control over what happens on the origin server. Since the server is maintained onsite, this model may take additional time and resources to fully implement.
- Offload model. Here, the origin server is placed on the CDN, outside the client network. Management capability is not quite as high, but maintenance needs are much lower because the company providing the CDN will take care of that, and you still fully control the content placed on your origin server. With this model, it is easy to have Mother clusters set up in order to hide the origin server from the Internet, and only have the Mother servers communicate with the outside world.
- Custom model. This model combines the customer origin and offload models. Static content is offloaded to the CDN, while dynamic content is kept locally and served from the origin server. The custom CDN model effectively gives the best of both worlds between the customer origin and offload models.
So when is a CDN useful? A CDN is useful when you have a lot of content that doesn't change very often – static content can be cached on the "edge" servers for users to pull from. If content is constantly changing, the caching servers will be updated constantly, defeating the purpose of caching. Because the caching servers will be sending multiple repeated requests back to the origin server, it may be more effective to have those requests go straight to the origin server from the user and strengthen the origin hardware to handle the requests.
For example: a stock ticker updates in real time, so there is nothing to cache. Movie sites, picture galleries and other static pieces are ideal for CDNs because they can be cached for long periods of time, closer to the user. Static content does not need to stay completely static, however; for each piece of content, a Time-To-Live (TTL) can be set so that when the specified time interval elapses, the caching server will send a request to the origin server to update the content.
Content Delivery Networks have a wide range of uses, from network scaling to Web site performance increase. There are times, however, where a CDN may not be the ideal solution. In essence, the more static content a site has, the more useful a CDN will be.
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