Definition
The CAP Theorem (also known as Brewer’s theorem) states that a distributed data store can only provide two of the following three guarantees: Consistency, Availability, and Partition Tolerance.
Why It Matters
It forces architects to make explicit trade-offs between consistency and availability during network partitions, which is fundamental for building reliable cloud infrastructure.
Core Concepts
- Consistency (C): Every read receives the most recent write or an error.
- Availability (A): Every request receives a (non-error) response, without the guarantee that it contains the most recent write.
- Partition Tolerance (P): The system continues to operate despite an arbitrary number of messages being dropped (or delayed) by the network between nodes.