A multi-CDN is the combination of multiple CDNs (content delivery networks) from different providers into a single network.
When used correctly, a multi-CDN can provide flexibility, availability, and performance benefits when compared to a single CDN. Understanding multi-CDN begins with understanding the benefits of CDNs in general.
CDNs play a vital role in serving and securing Internet traffic across the globe. By using a CDN, businesses can reduce demand on origin servers, protect against DDoS attacks, and improve performance.
Different CDN providers offer users access to a different network of Points of Presence (PoPs), different underlying network infrastructure, and different sets of specialized features. As a result, different CDN providers may also deliver different performance, security, and cost benefits depending on workload and geographical location. Multi-CDN enables businesses to use “the right CDN for the job” by allocating specific workloads to specific CDNs.
Additionally, any single CDN has a finite capacity and individual PoPs or even entire CDNs may fail. A multi-CDN allows capacity from different to be combined and enables fault tolerance in the event of failure.
Multi-CDNs work by selectively routing traffic over different CDNs in the network. The specific criteria around what routing decisions get made varies between multi-CDN implementations. Common multi-CDN strategies include:
The pros of multi-CDN strategies are gains in performance, resilience, and flexibility. The most obvious con is increased network complexity. Each new CDN brings with it additional management interfaces & APIs, functionality, and administrative tasks. While some of the complexity can be abstracted away by a multi-CDN broker, the underlying network topology is still more complex with multi-CDN.
We’ve intentionally left cost off our list of pros and cons. It is true that one CDN is cheaper than two if all else is equal. However, there is a valid counterargument that multi-CDN enables better overall vendor management and cost control.
The larger and more sensitive to downtime and/or latency your application is, the more likely the pros of multi-CDN are to outweigh the cons. Similarly, once you decide to use multi-CDN, the choice of how to implement it depends on the same criteria. For some cases, where some manual intervention is acceptable, static DNS entries may be enough. On the other end of the spectrum, a more variable-driven load balancing approach may be worth the upfront cost and complexity.
As the engineering team at Mux, creators of the Mux Video API, demonstrated the StackPath CDN can be an important part of a high-performance multi-CDN. StackPath can also provide the infrastructure to build your own extensible and scalable variable-driven multi-CDN.
For example, users can deploy DNS resolvers using Edge Computing Workloads. Resolver logic is configured to route across CDNs based on custom user-defined logic, and Anycast IP addresses simplify configuration and ensure requests are routed to the nearest StackPath Edge location