In-depth Investigation of CDN: Part 1
Learn push and pull models and dynamic content cache optimization in CDNs.
We'll cover the following...
In this lesson, we’ll go into the details of certain concepts, such as CDN models and multi-tier/layered CDN architecture, that we mentioned in the previous lessons. We’ll also introduce some new concepts, including dynamic content caching optimization and various techniques to discover the nearby 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 CDNs 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 the CDN. The content is pushed to proxy servers 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 keep the files for a specified amount of time and then remove them from the cache if they’re no longer requested to balance capacity and cost.
When users request web content in the pull CDN model, 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, the 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 the pull CDN, thus improving availability. On the other hand, the pull CDN is favored for frequently changing content and a high traffic load. Low storage consumption is one of the main benefits of the pull CDN.