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What is a CDN?

A CDN (a content delivery network) is a geographically distributed network of servers that work together to load web resources faster based on the proximity to the user. A CDN is the best way to speed up your site performance[1].

A content delivery network is not the same as a web host. Traditionally, web hosting relies on one server in one location which is responsible for showing 100% of your website content to the client. CDNs are scattered around the globe and store cached copies of your content, and the goal of CDNs is to provide better accessibility of this content.

CDNs are widely used by video and live streaming platforms, e-commerce, mass media, social media, software services, etc. Companies like Amazon, Netflix, and Facebook use CDNs.

How content delivery networks operate

Generally speaking, a content delivery network includes data centers in different locations around the globe and ‘points of presence’ (PoP) (which are not necessarily physical), performing cache-only functions. 

The root server mirrors content to other servers within the content distribution network. When a user (a client, which is any web browser) loads a web page, HTTP requests are sent to the server. The client request is rerouted to those servers, and the nearby server in the CDN gives out the cached copy of the content.

When a website operates on a CDN, the dynamic content which should be loaded every time anew will be presented from the website, while other rich web content from the page (static content, usually CSS, graphics, images) can be loaded from a cached copy stored on the closest CDN server.

Why do you use a CDN?

First of all, CDNs can be an affordable way to provide high-quality services without splashing out on heavy internal solutions. This is vital for companies covering large geographic areas and offering rich web content.

The goals of using content delivery networks are multifold. Namely, CDNs are used to:

Reduce latency

The response time of the server is shorter, the content cached on CDNs can be loaded quicker, which means that overall user experience improves.

Decrease network congestion and bandwidth costs

Incoming requests are routed to different destinations, a part of content is loaded from the site while the rest is served from the CDN in a different area; thus, the web traffic flow is redistributed.

Optimize the workload on servers

The web host has more capacity to process requests for serving the dynamic content while the static content is served from CDNs; thus, CDNs minimize timeouts and jitters that occur due to connection interruptions.

Ensure content availability

If one data center breaks down, the same data can be retrieved from a different node;  the way CDNs operate minimizes the potential negative impact of DDoS attacks.

Enhance security

Modern CDN service providers offer additional protection by encryption, private CDNs, analytical data, etc.

What are the benefits of CDNs for SEO?

CDNs carry some tangible benefits for SEO. CDNs can improve page load time which means the page takes a higher score on the PageSpeed test and meets the Core Web Vitals thresholds. Thus, a CDN can be a good solution for SEO to increase site performance which, in turn, can impact rankings.

Moreover, a content delivery network ensures that the user reaches a cached copy of content on a replica server from a different location in case it misses from the nearby PoP. Coupled with enhanced stability with traffic surges, all this ensures better availability and accessibility of content.

Finally, there should not be any duplication issues because CDNs use canonical headers to refer search engines to the original content on the origin servers.

Types of CDNs

There are many ways how CDNs are implemented. Among those, one could single out the following CDN types:

  • Peer-to-peer CDNs
  • Private CDNs
  • Virtual CDNs
  • Image CDNs

CDN checker tools

There are CDN finder tools able to detect if a site uses a CDN, for example, CDNPlanet. Such tools use different technical means to check for availability of a CDN provider on a website:

  • Load and render the page and inspect the resources
  • Fetch a page resource and inspect the response headers (mostly for the server header)
  • Finding some other unique identifying header (e.g. lswcdn-country-code for Leaseweb)
  • Perform a DNS lookup and inspect the full CNAME chain
  • Look up the name of the network the server IP(s) belong to

CDN service providers

There are many CDN providers, both open source and commercial that differ by the scope of services and pricing.

For example, Wikimedia, a media database behind Wikipedia, has its own caching solution based on open source software[2]. Other famous CDN services are:

  • Cloudflare
  • Amazon Cloudfront
  • Edgio
  • Akamai
  • StackPath
  • Limelight
  • Fastly
  • ArvanCloud
  • Kingsoft Cloud
  • Coral

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