The Multi-CDN Strategy


The multi-CDN strategy has been in play for only a few years. Seven years ago, very few companies used dual CDNs. I rarely encountered high Alexa ranked websites using two or more CDNs, and that includes Tumblr and LinkedIn. That has definitely changed now. In the past, the main reason the Internet companies didn’t use two CDNs was the simple fact that they were new to the CDN ecosystem. However, as the Internet traffic for many of these websites skyrocketed to tens of millions of monthly users, the executive mindset started to change.

These hot Internet startups reached valuations into the hundreds of millions of dollars, and sometimes billions of dollars. Their entire existence depended being online 100% of the time. Downtime was unacceptable. Even though a CDN like Akamai could provide 100% uptime, it wasn’t best practices to put all the eggs in one basket. As these Internet companies increased their knowledgebase of the CDN ecosystem, they started using multi-CDNs in their environment. There are a few rules of thumb when deploying multi-CDNs.

How Many CDNs Should Be Used

For starters, selecting the right number of CDNs depends on the type of online property. Heavy video sites require more CDNs. eCommerce can get by with one, unless your eBay. needs one CDN, LinkedIn needs three CDNs, and Netflix needs four CDNs. In terms of complexity, managing multiple CDNs is not as difficult as it sounds. If two CDNs are being used, than two control panels, two reporting systems, and two setup configuration tools must be learned. The more complex features like DSA, and FEO must be configured by the CDN.

However, the concept and meaning of the CDN features are the same for all CDNs. TTL, query strings, live streaming publishing points, VOD setup, and so on are similar in concept, and result in the same outcome. If a company becomes an expert in using Akamai, than learning the ins-and-outs of EdgeCast, Limelight or Fastly, shouldn’t be difficult, just time consuming. In terms of price, using two or more CDNs is great for the customer, because they can leverage each CDN against each other to get the best deal possible. There won’t be much price gouging.

In addition, services such as DNS load balancing makes it easy for the CDN customer to slice and dice traffic, allocating  a certain percentage to each CDN in the multi-CDN deployment. The most difficult challenge in using multi-CDNs is selecting the right CDN for the job. Just as I stated many times in my blog, CDNs are specialist. Some CDNs work well with eCommerce, others with live streaming, others in security and DDoS protection, and so on. If I were CTO of the companies below, this is the number of CDNs that would be used.

 The Multi-CDN Strategy  Examples
  • Netflix: 4 CDNs: Akamai, Level 3, EdgeCast and Limelight
  • Facebook: 3 CDNs: Akamai + 2 others
  • LinkedIn: 3 CDNs
  • Twitter: 3 CDNs
  • World of Warcraft – 3 CDNs: Akamai + 2 others
  • Hulu: 2 CDNs
  • Overstock: 2 CDNs
  • Walmart: 2 CDNs
  • eBay – 2 CDNs
  • Oracle: 2 CDNs
  • SAP: 2 CDNs
  • Microsoft: 2 CDNs
  • AVG: 2 CDNs
  • ESPN: 2 CDNs
  • Dreamworks: 1 CDN
  • Lions Gate: 1 CDN
  • TMZ: 1 CDN
  • 1 CDN
  • 1 CDN
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