Explain the CAP Theorem in one paragraph

Question

Explain the CAP theorem. In a network partition, which two properties must you choose between?

Answer

CAP states that a distributed data store can guarantee at most two of: **Consistency** (every read sees the latest write), **Availability** (every request receives a non-error response), and **Partition tolerance** (the system continues despite network splits). Since partitions are unavoidable in real networks, you effectively choose between C and A *during* a partition. CP systems (e.g., etcd, ZooKeeper) reject writes to preserve consistency. AP systems (e.g., Cassandra, DynamoDB with eventual reads) keep serving but may return stale data. Modern systems tune this per-operation via consistency levels rather than picking one label globally.