CDN

CDN is an abbreviation for Content Delivery Network.

It is a group of servers spread out over many locations.

These servers store duplicate copies of data, generally are the static resources, such as images, css files, js files.

POP

POP(point of presence) is a single geographical location where a group of CDN edge servers reside.

Edge server

An edge server, which is a server that resides between two networks, are located at each POP. Edge servers do not generate content for the website, instead, they keep a copy of the content in the cache.

Why

1. CDN can fulfill data requests based on which servers are closest to the end-users, ensuring a faster response and download time of content due to reduced latency.
2. It lowers the request burden on our own servers.
3. Cache. Same file will not be downloaded again if user has visited same CDN which requires this file.
4. Good CDNs can offer higher availability, lower network latency and lower packet loss.
5. Boost reliability, If one edge server is not available, requests are automatically sent to the next available edge server.
6. Many commercial CDNs provide additional features, e.g. usage analytics, security
7. Page speed is a very important factor for SEO(search engine optimization)
8. Load balance between multiple servers

Type

• Public
• Private
• Paid
• Free

How

The idea is to direct the user to the closest point of presence. When a user requests content from a site that uses a CDN, the request is routed to the closest POP, where a web server sends the requested data. There are several different ways that a request can be routed to a specific POP, one of which is IP Anycast.

Reverse Proxy

CDN employ reverse proxy technology.

This means CDNs are deployed in front of your backend server(s).

This position, on the edge of your network perimeter, offers several key advantages beyond a CDN’s innate ability to accelerate content delivery. For example, security, load balance.

Push vs. Pull Zones

Most CDN providers offer two ways of caching your data: pull zones and push zones.

Pull

Pull Zones involve entering your origin server’s address, and letting the CDN automatically fetch and cache all the static resources available on your site. Pull zones are commonly used to deliver frequently updated, small to medium sized. After providing the CDN with your origin server’s address, the next step is usually rewriting links to static assets such that they now point to the URL provided by the CDN. From that point onwards, the CDN will handle your users’ incoming asset requests and serve content from its geographically distributed caches and your origin as appropriate.

Push

To use a Push Zone, you upload your data to a designated bucket or storage location, which the CDN then pushes out to caches on its distributed fleet of edge servers. Push zones are typically used for larger, infrequently changing files, like archives, software packages, PDFs, video, and audio files.

Evolution

Static CDN

-> Dynamic CDN(static and dynamic content, including rich media)

-> Multi-Purpose CDN(static and dynamic content, including mobile and rich media)