Multi-CDN delivery has been growing in popularity for a variety of reasons, ranging from security to performance to simply updating legacy architecture.
For companies that deliver content via live streaming though, there are unique reasons to consider multi-CDN. Real-time performance insights, automation, on-the-fly control and flexibility, and — most of all, quality of experience — are crucial to success. Let’s explore why you should evaluate multi-CDN and what key factors to consider in doing so for your quality of experience (QoE) goals.
QoE benefits of multi-CDN delivery
Beyond high availability and network redundancy, multi-CDN delivery also enables providers to adapt to changing network conditions with multiple delivery paths to the viewer:
Geo-coverage and optimizations: Delivery networks differ in characteristics and coverage geographically. Understanding these differences and where one network might be more performant provides a key lever in QoE.
Eyeball network optimization and coverage: Closely tied to geo-coverage, edge delivery networks may not reach eyeball networks the same way. These differences can allow a broadcaster to route around network congestion to avoid jitter, latency, or other adverse QoE conditions.
Peak traffic capacity, on-demand: Multi-CDN delivery allows a broadcaster to leverage all the peak capacity available to each edge provider simultaneously. Some providers will also provide reserved capacity for peak events.
A clear vision of your fan experience goals should drive how you leverage these benefits. For example, the best delivery path is not necessarily measured just by latency. A 4K stream requires significantly more throughput than a 1080p stream. A low-latency stream experience is much less tolerant of network jitter, which can cause rebuffering. Multi-CDN delivery allows you to select the optimal path for the performance profile based on your specific QoE goals.
Key considerations for multi-CDN delivery
The QoE goals you focus on should also dictate your multi-CDN vendors — including understanding what vendor-specific features you might have to give up or normalize across all of them. Here are a couple QoE considerations to keep in mind when choosing CDN vendors:
Traffic management: The fundamentals of multi-CDN delivery require a traffic management layer. Your QoE goals will influence what criterion drives a CDN switch and whether you select DNS, the player, or server-side manifest manipulation to route traffic to each edge provider.
But it is equally important to consider how each CDN and the aggregate of all of the providers in your architecture will impact your origin infrastructure. Consider that AWS Elemental MediaStore, a high-performance cloud storage system designed for low latency live stream, can handle 1,000 requests per second. Some CDN providers have thousands of mid-tier servers that provide caching hierarchies to reduce the impact of massive requests for new objects. In live video delivery, every segment is a new object. And the manifest itself is a newly refreshed object that must be accessed by the player constantly. In a multi-CDN delivery deployment, this could mean 10s of thousands of requests going back to your MediaStore every second--several times more than what it can handle.
Protecting your origin from this load is critical to maintaining availability to the stream. Products like Fastly’s Media Shield provide this critical origin offload, further collapsing the requests of many mid-tier CDN servers to just a few per second going back to origin infrastructure.
Observability: In order to determine success, you need to be able to see what’s going on. This is not just having monitoring or analytics. It is having a complete picture of what’s going right and wrong, where that’s happening and why. Commonly referred to as observability, this methodology in DevOps practices translates to streaming with significant benefits.
Of critical importance, real-time stream switching requires observability on every downstream delivery component, from each CDN to the player to the ad ecosystem (if that’s a factor). Note that some CDNs do not provide real-time logging critical to this workflow. Fastly’s Media Shield provides real-time logging in multi-CDN deployments for downstream CDNs.
Where to go from here?
The most important thing to remember as you’re architecting multi-CDN delivery is to understand your primary motivation for choosing this in the first place and ensuring that your application, infrastructure, and engineering teams are in a position to make your implementation successful.
Ready for more info? Check out this multi-CDN delivery survey we did on barriers, drivers, and strategies, to help drive your thinking. Also, if you’re interested in CDN performance, read our VP of Technology’s posts on performance testing and how to better measure cache hit ratios.