The machine is the easy part. Address reputation, geolocation and an abuse process that answers decide whether the service works at all — then conntrack, MSS clamping and IPv6 decide whether it scales past one node.
A game server is a simulation loop with a fixed deadline, and no amount of cores makes one thread finish sooner. What to buy for a single instance, what to buy for density, and why jitter beats port size.
The edges take the load until a purge, a deploy or a cold region sends every one of them to the origin at once. Hit-ratio arithmetic, the cache headers that are the whole contract, and which machine to actually build.
A broken AAAA record does not take a site down, it makes it slower for everyone who has IPv6. The prefix you get, the static configuration to prefer, the three things that break it, and how to prove it works.
All three are still shipping because they solve different problems. The interface ceilings, the queue models, the DWPD and power-loss specifications that actually matter, and how to pick the mix for your working set.
Every dedicated machine ships with out-of-band access, so a reinstall is yours to run at 3 a.m. without a ticket. The order of operations, and the three places it usually goes wrong.