Based on context, you are insinuating that a discussion board like HN _can_ be hard on the CPU alone? If so, how? My guess would be _also_ be that the CPU would have little to do by itself, but that I/O would take the brunt?
Negotiating TLS handshakes is one way. But I'd imagine the rest is largely IO-bound like you said.
It still puts into perspective what a big pile of dogshit consumer software has become that stuff like this comes as a surprise. Also, the last time I checked, Let's Encrypt also ran on a single system. As did the Diablo 2 server (I love reading about these anecdotes.)
For every incremental change in HW performance, there is an order-of-magnitude regression in SW performance.
If nothing else, handling interrupts from the NIC to pull packets out of its receive buffer, though that should be usually be isolated to a couple of cores.
Also, re: I/O, the CPU usually also has to handle interrupts there, as well as whatever the application might be doing either that I/O.
> If nothing else, handling interrupts from the NIC to pull packets out of its receive buffer,
Interrupts? Interrupts? We don't need no stinking interrupts! https://docs.kernel.org/networking/napi.html#poll