While Content Delivery Networks (CDNs) help improve video streaming performance dramatically, they're not perfect or equally performant at all times. Some CDNs are better in specific regions where they've invested more or have better relationships with the local Internet Service Providers (ISPs). Some CDNs have acceptable performance in popular areas while also costing much less. And like any service, CDNs can sometimes have outages.
Multi-CDN refers to using multiple CDNs to deliver video (and other content) more reliably, performantly, and/or affordably, depending on your specific goals. The process involves taking constant measurements of CDN performance and deciding which CDN is "best" in real-time. A common strategy is to:
- Use the most affordable CDN in times and regions where all CDNs are all performing comparably
- Use the best performing CDN where and when it makes an impactful difference for viewers (often based on Quality of Experience metrics)
- Fail over to backup CDNs when primary CDNs experience outages
Often the contractural volume commitments to CDNs is considered as well, meaning a specific CDN will be favored until the commitments are satisfied.