DNS

How this question breaks down

1. 1ResolutionCore20 minA recursive resolver turns a name into an address by walking delegations from the root to the zone that owns the name, then remembers every answer it collected on the way.
2. 2CachingCore19 minEvery answer is cached by several layers for as long as its TTL says, so the TTL decides how fast changes spread, how much load reaches your nameservers and how long you survive their outage.
3. 3GeoDNSCore17 minAn authoritative server that answers differently depending on who is asking can send each user to a nearby, healthy or cheaper site, as long as it can tell where the user really is.
4. 4FailoverCore18 minHealth checkers watch each site and the nameserver stops handing out a dead one, but users only move once detection, publication and every cache's TTL have all run their course.

Work through the parts in order and you’ve covered the full design. Each part is one topic.