Just spaces CDN, not spaces - you'd think they'd just turn the CDN off for a bit.

You can't just "turn off CDN" on the modern internet. You'd instantly DDOS your customers' origins. They're not provisioned to handle it, and even if they were the size of the pipe going to them isn't. The modern internet is built around the expectation that everything is distributed via CDN. Some more "traditional" websites would probably be fine.

Might be just me, but I can think of many origins under my control which could live without a (non-functional) CDN for a while.

CDN is great for peak-load, latency reductions, and cost - but not all sites depend on it for scale 24/7

If you are DO you could, you just decided not to bother. They control the origins it's spaces (s3), so they could absolutely spin up further gateways or a cache layer and then turn the CDN off.

Either you are wrong and they do not have the capacity to do that, or they have decided it is acceptable to be down because a major provider is down

I imagine a cache layer cannot be that easy to spin up - otherwise why would they outsource it?

You outsource it because clouflare have more locations than you so offer lower latency and can offer it at a cost that's cheaper or the same price as doing it yourself.

Which suggests its expensive enough for it to be unlikely they just have the capacity lying around to spin up.

To the contrary, CDN pricing will usually beat cloud provider egress fees.

Common example: you can absolutely serve static content from an S3 bucket worldwide without using a CDN. It will usually scale OK under load. However, you're going to pay more for egress and give your customers a worse experience. Capacity isn't the problem you're engineering around.

For a site serving content at scale, a CDN is purpose-built to get content around the world efficiently. This is usually cheaper and faster than trying to do it yourself.

That is not what I said. I said DO will not have the spare capacity because its too expensive. Can you please tell me who DO pay egress fees to?

They will be doing a mix of peering both across free PNIs and very low cost IXP ports, with the reminder going down transit like Colt or cogent. Probably average cost of the order of about $1 per 20TB of egress in Europe and NA markets.

The thing is with edge capacity is that you massively overbuild on the basis that;

It's generally a long ISH lead time to scale capacity (days not minutes or hours).

Transit contracts are usually 12-60 months

Traffic is variable, not all ports cover all destinations

Redundancy

So if you are doing say 100Gbps 95%ile out of say London then you will probably have at least 6+ 100Gb ports, so you do have quite a bit of latent capacity if you just need it for a few hours.

nit: that's more DoS (from a handful of DO LBs) than DDoS.