But CDNs are made for static content so your comment means I can't run a dynamic website unless I have unlimited file descriptors and flawless connectivity.

"Need" is a strong word. But I think the point is that if you expect wildly spikey traffic/don't want the site to go down if it receives a very sudden influx of requests, going static is a very good answer, much cheaper than "serverless" or over-provisioning.