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> except all this does is to shift the SPOF from CDN to CDN selector so doesn't solve the problem.

True, except we've just moved the SPOF from a complex TCP stack (your HTTP(s) service) receiving direct user-connections, to a much less complex UDP stack that benefits from widespread downstream caching.

Is it still a SPOF? Yes. But it's also one that is much less complex, and less likely to go wrong.

> Larger sites need to consider for example test coverage, troubleshooting, logging etc. which are all far more complex on multi-CDN.

They are more complex, they are not "far" more complex.

There might, of course, be an engineering cost in getting to the point that you can do multi-CDN properly, safely, but ultimately your tests should be CDN agnostic, and you should have well-defined troubleshooting workflows that minimise/mitigate the complexity there.

Logging - if pulling logs from different sources is an issue for you, then it's not multi-CDN you've screwed up, it's your logging pipeline. If you can find a CDN provider that doesn't expose an API for you to pull logs via, then you've just found a CDN provider that you shouldn't be using.

> Thinking you can just re-point a CNAME is, well, wishful thinking.

Now you're misstating what I said

'With a *good* CDN switcher, you essentially just have another CNAME in the DNS chain - all CDNs respond to the same host header, and your switcher just routes traffic to different CDNs based on observed/learned status as well as your preconfigured ruleset.'

That's not saying "you can just repoint a CNAME".

> And that's not even touching on large services that need to do capacity planning with the CDNs and take selector decisions based on load.

That ability to configure that is built into pretty much every good CDN switcher.

Yes, you need to do some planning with the CDNs themselves to discuss what load you're going to send, as well as getting details of how they expose metrics for your switcher to consume. If you're big enough to need a switcher though, then you're more than big enough to be having those conversations.

This stuff _really_ isn't as complicated as you seem to think - it just needs a bit of planning and forethought.