Trees & Graphs

Graphs show up less often than the rate limiter or the cache. But when they do, Cloudflare tends to frame them as the thing it runs: a mesh of data centers with links between them. Each of those data centers is a point of presence, or PoP, one of the many locations Cloudflare operates in cities worldwide so that a visitor is served from close by. Model the PoPs as nodes and the links as edges and most of the graph questions in the loop become recognizable.

Three moves cover almost all of it. You order a set of things by what they depend on. You find the cheapest route from one node to the rest. Or you merge nodes into connected groups and watch for the moment a new link closes a loop. The substrate is textbook, so the interview pressure sits elsewhere. You have to spot that a pile of config or a propagation delay is really a graph, pick the traversal the question points at, and handle the follow-up the interviewer adds a minute later.