In-depth Investigation on CDN (Part 1)

In this lesson, we will go into the details of certain concepts (CDN models, multi-tier/layered CDN architecture) that we alluded to in the previous lessons. We will also introduce some new concepts—dynamic content caching optimization and various techniques to discover the near proxy servers in CDNs.

Content caching strategies in CDN

Identifying content to cache is important in delivering up-to-date and popular (web) content. To ensure timely updates, two classifications of CDN are used to get the content from the origin servers.

Push CDN

Content gets sent automatically to the CDN proxy servers from the origin server in the Push CDN model. The content delivery to the CDN proxy servers is the content provider’s responsibility. Push CDN is appropriate for static content delivery, where the origin server decides which content to deliver to users using CDN. The content is pushed to proxy servers located in various locations according to the content’s popularity. If the content is rapidly changing, the push model might struggle to keep up and will do redundant content pushes.

Pull CDN

A CDN pulls the unavailable data from origin servers when requested by a user. The proxy servers will keep the files for a specified amount of time and then remove them from the cache if they are no longer requested to balance capacity and cost.

When users request web content in the Pull CDN, the CDN itself is responsible for pulling the requested content from the origin server and serving it to the users. Therefore, this type of CDN is more suited for serving dynamic content.

As stated, Push CDN is mostly used for serving static content. Since static content is served to a wide range of users for longer than dynamic content, the Push CDN scheme maintains more replicas than Pull CDN, thus improving availability. On the other hand, Pull CDN is favored for frequently changing content and a high traffic load. Low storage consumption is one of the main benefits of Pull CDN.

Most content providers use both Pull/Push CDN caching approaches to get the benefits of both.

Dynamic content caching optimization

Since dynamic content often changes, it is favorable to optimally cache it. This section deals with the optimization of frequently changing content.

Certain dynamic content creation requires the execution of scripts that can be executed at proxy servers instead of running on the origin server. Dynamic data can be generated using ...