Have to disagree here, you can have very different performances from different CDNs for the same user at the same time. Some CDNs have their own backbone (or at least partially), a lot of them are using different routes, and a lot of the time, the issue is not with the backbone, but with peering inter-connections, which can be different between each ISP & CDN. And a CDN's capacity is shared between all its customers, so if you get a huge peak from one of them, it can impact the others too.
Old but good example: Before Apple started building out its own CDN, it was using the leading commercial one, and when Apple was doing its iOS/MacOS updates, other broadcasters were having big troubles delivering their streams at the same time because the CDN was overloaded - but it doesn't mean that other CDNs were also all down.
That's also why most video broadcasters are now doing multi-CDN for their biggest live events like Superbowl or the world cup - to be able to distribute the load on several networks.
In this case - given this and the other comments - I stand corrected!
I would love to see some data on examples of this occurring in the wild - and it 100% makes sense that a congested CDN provider would impact neighbors. It would be great if someone could do a writeup on examples and the detection/mitigation strategies. Perhaps issues like these (alongside cost) are driving the DIY CDN adoptions (Apple being the exemplar but also Tesla etc)?
Also the Pinterest example is a great real world example - and they do an awesome job especially given the size of that cache - so there must be so real value from a performance standpoint!
Out of curiosity does it seem like these dynamic switching decisions are better at the server level or client level?
