Is Multi-CDN Always the Answer for Five-Nines Uptime Streaming at Scale?
Taking a multi-CDN approach would seem to be a no-brainer for delivering large-scale streams to global audiences and maximizing uptime in the face of bursts, unexpected regional demand, and other impediments to a smoothly delivered high-stakes stream. But Bob Hannent, Principal Architect: Technology Operations, DAZN, says it’s not always so, and a multi-CDN approach can actually introduce inefficiencies, in this discussion with Mark de Jong, Chairman, CDN Alliance at Streaming Media Connect 2023.
De Jong says, “I think more than 60% of all the bigger providers are relying on multi CDNs.” He asks Hannent, “Is that working in terms of the line of defense of using multiple CDNs to get close or get to the five nines?”
Hannent says that thinks it is essential to use multiple CDNs to work at DAZN’s scale. However, he notes that it is not always the case depending on the type of programming and the expected size of the audience. “We do competitive fishing, and we do competitive lumberjacking,” he says. “So if something has a low viewing audience, maybe you can get a better delivery out of a single CDN. But the moment that you start to get to really popular content, [such as] Italian football, you cannot go without having multi-CDN.”
But Hannent notes that vendor resilience is also essential due to a number of unpredictable factors. “The worst thing that can happen is Apple makes a software release, a new game is released on Steam, or you get caught by something happening on Xbox,” he says. “You've got to be really careful. So, the bandwidth and the geography of the internet can change even during a game. You need that vendor resilience. You need the ability to change direction.”
Live delivery at a large scale is the major factor in needing multi-CDNs, Hannent says. “VOD’s easy,” he says. “We always say Netflix has got it easy. If you're delivering static or quasi-static elements and are used to doing that, that's great. But when you're trying to deliver live, everyone is watching at the live head, and everyone is asking for the same file at the same second, and that creates massive inefficiencies in the CDN. So it means your callbacks and your requests back to your origin…the intermediate parts in the CDN just don't know that the request has already been made. Even the same process in the same machine, in the same node, doesn't know that the same request. You've got these race conditions that go on, and that means you do need a lot more capacity all the way through the supply chain than you'd think you need. It can be a factor of over five times more capacity that you need than you think you need.”
De Jong says, “Having multiple CDNs also stresses more in terms of your middle caching layer and your origins because you have more requests back.”
Hannent agrees. “Your origin caches have to be bigger,” he says. “Your grandfather tier is getting hit more and more, so there's a map all the way through the supply pipeline. You can get hit, but as I say, if you apply multi-CDN where you don't need it, you also get inefficiencies in your system.”
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