Distributed Systems Architecture

CAP Theorem

The fundamental theorem stating that in the presence of a network partition (P), a distributed data store must choose between Consistency (C) and Availability (A).

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Deep Dive

How CAP Theorem Works in Production

Under-the-hood mechanics and technical implementation details.

Technical Deep Dive

Detailed Architecture

Formulated by Eric Brewer, the CAP Theorem proves that a distributed system cannot simultaneously guarantee: Consistency (every read receives the most recent write or an error), Availability (every non-failing node returns a non-error response without guarantee of latest write), and Partition Tolerance (the system continues to operate despite arbitrary message loss or delay). Since network partitions are an inevitable physical reality in distributed networks, systems are classified as either CP (e.g. HBase, CockroachDB, Raft/Paxos clusters) or AP (e.g. Cassandra, DynamoDB with eventual consistency).

Key Architectural Rule / Formula:

Network Partition (P) is mandatory in distributed networks; choose CP (strict consistency) or AP (high availability).

Engineering Trade-Offs

Trade-Off Dimensions & Analysis

Evaluating advantages and drawbacks during architecture interviews.

Dimension	Advantages (Pros)	Drawbacks & Costs (Cons)
CP (Consistency + Partition Tolerance)	Guarantees strict linearizability and zero stale reads across nodes.	Refuses requests or returns errors if nodes cannot reach consensus during a partition.
AP (Availability + Partition Tolerance)	Always returns a response to the client even if replicas are temporarily isolated.	Clients may read stale data; requires conflict resolution mechanisms (Vector Clocks, CRDTs, LWW).

Interview Application

How to Frame CAP Theorem in System Design Rounds

Senior-level talking points and related interview problems.

Interview Strategy

Evaluating in Loops

Evaluated in every senior system design round when discussing database selection and multi-region replication architectures.

Applied System Design Scenarios

Payment Gateway & Financial Ledger
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