What Is a Multi CDN?

Using a multi CDN, or dynamic CDN is the process spreading a website's static content across the servers of multiple CDN providers to further increase global presence. With each CDN provider's servers being available to deliver content, website latency is able to be further reduced for more users in various geographic regions. Having a multi CDN setup in place also helps improve redundancy as if one CDN provider's network goes offline, the content will continue to be delivered from the alternative providers.

This article focuses on how a multi CDN works as well as what the benefits and drawbacks are of using one. For more general information about what a single CDN is and how it works, read our How Does a CDN Work article.

Who is using a multi CDN?

The multi CDN strategy has only recently begun to gain traction over the past few years. For large Internet-based companies which deliver content to users around the globe, making use of a multi CDN has proven to be quite beneficial.

Based on Dyn, the top five industry CDN users are also multi CDN users.

These industries deliver vast amounts of content to users across the globe and using a multi CDN can help improve the efficiency of that process. It is no surprise that Internet/computer software and media companies are among the top two industries using single and multi CDNs. Companies that stream large media files to their users are able to take great advantage of the widespread global presence of a multi CDN setup. Additionally, software companies like to push their most recent updates to users via a CDN as they will be delivered faster.

Netflix for example uses three CDNs to deliver it's media streaming services to users around the world. YouTube and many other well-known, large technology companies also implement the use of multiple CDNs.

How does it work?

There are two separate options that can be used to setup a multi CDN configuration. The following section explains how both options work and what is involved in using each.

CDN aggregator

A CDN aggregator combines the functionality of various CDNs and is controllable via one main control panel. There are both benefits and downsides to this. On one hand, you are not required to modify each CDN specifically, which in turn reduces the amount of time required to make a change. On the other hand, this hinders the customizability of each CDN as they are all aggregated into one central control panel.

This method is desirable for companies who aren't seeking to do much customization and don't have a great deal of resources to associate with the administration of a dynamic CDN.

Load balancer: Amazon Route 53

The second option for implementing a multi CDN is to use a load balancer service such as Amazon Route 53. Load balancing is the process of efficiently distributing user requests across multiple servers in order quickly deliver content to a user based on their region as well as to avoid overloading a single server.

Load balancing for a multi CDN is used to distribute requests to the most optimal server within the cluster of servers across various CDNs. Therefore, if a user makes a requests from France their request will be routed to the CDN who's servers are closest to France. Similarly, if a user makes a request from North America, their request will be routed to the most optimal server in the effort to reduce latency times.

Benefits of using a multi CDN

There are obvious benefits to using a multi CDN. The following list describes a few of these benefits:

• Redundancy: if a CDN provider goes down, traffic gets rerouted to another provider's servers
• Increased global presence
• Additional features from each CDN
• Some CDN providers are better for specific content delivery (e.g video streaming)
• Reduced latency for users that otherwise would not be as close to a server

Taking advantage of multiple CDN providers' server locations / performance benefits can be of great value. These advantages are a major reasons why large global companies are adopting the use of dynamic CDNs.

Drawbacks of using a multi CDN

There are also a few drawbacks in using a multi CDN. These drawbacks can include:

• Added complexity
• Added administrative duties (if using the load balancing method)
• Additional costs required (load balancer service / CDN aggregation service / higher costs of CDN providers)
• Total cost of ownership and maintenance of a multi CDN is quite high

These drawbacks make is apparent that a multi CDN solution is often not the answer for small, medium, or even certain large sized companies. A website should be receiving a substantial amount of traffic from various locations spread across the globe before beginning to investigate the possibility of implement a multi CDN.

What are federated CDNs?

A federated CDN is different from a multi CDN in that they allow service providers to use preexisting infrastructure to in a way, build their own CDN. Federated CDNs allow service providers to lower costs by pooling resources, minimizing complexity for content providers, and enhancing the consumer's quality of service

Federated CDNs have the objective to:

• Give content providers better control over their content distribution and allow them to offer a better experience to end users
• Reduce network transport costs
• Allow service providers to that don't specialize in CDNs to create a content delivery network
• Simplify business and technical agreements with content providers.

To learn more about CDN Federations, read Cisco's content delivery network (CDN) Federations white paper.

Summary

In summary, multi CDNs are a fantastic solution for distributing content across more servers in even more geographic regions. For the right companies, this method of content distribution is very efficient as users around the world will have more or less equal access to the same speeds.

However, before considering the addition of a multi CDN structure, website owners should first pinpoint website performance issues that may be easily corrected. This may be result in enough of a performance increase to avoid opting for a multi CDN although if not, an internal audit based on a company's needs and goals should be undertaken. This will help determine if a multi CDN solution is required or if a single CDN will deliver the required performance without the added complexity.