The Split-Brain
PagerDuty — conflicting customer data across DCs
3-node cluster: Network partition isolated Node C. All nodes kept accepting writes (AP). Alice's email updated in us-east, phone in eu-west — clients see different profiles.
The trap: Split-brain with no quorum check — both partitions think they're leader.
Your task
Fix `DistributedNode.write()` and `reconcileData()` in `distributed_store.js`: CP mode rejects writes without majority; MVCC/LWW reconciliation when partition heals.
Book: CAP theorem trade-off · Prod: AP for profiles, CP for payments — know your business requirement.
Skills you'll prove
Interview Tip
When asked about CAP, say: "The CAP theorem states that during a network partition, you must choose between consistency and availability. I've seen this in production — a network partition between data centers caused a split-brain where both sides accepted writes. We chose AP for user profiles (accept writes, reconcile later) but CP for payment processing (reject writes, prevent double charges). The key is knowing which trade-off your business needs."