Netlify are on multiple providers, but due to the DNS spec being old ( no CNAMEs at root) many providers respecting it without providing CNAME flattening, in some cases you have to give use a regular old IP as an A record, hence the impact of the GCP load balancer being down.

If one was using CNAME flattening, there was zero impact.

Why not 3? It is about how paranoid you want to be about uptime. Uptime and production grade are two different things. There is certain uptime guarantees that a cloud provider will give. Production grade is durability of the product itself.

Algorithms that tolerate Byzantine failures generally require t<n/3, i.e. at least 4 nodes to tolerate 1 byzantine fault. This is in fact required for primitives as simple as reliable broadcast. Systems that use leader election such as Raft are not Byzantine tolerant. They tolerate t<n/2, meaning that 3 nodes does indeed buy tolerance to 1 crash, but it doesn't support anything else than crashes.