Explain Pub/Sub vs RPC.

Pub/Sub (publish-subscribe) is an asynchronous one-to-many messaging model, while RPC (remote procedure call) is a synchronous one-to-one request-response communication method.

When to Use

Use Pub/Sub when multiple services need to react to an event independently — ideal for microservices, analytics, or notifications. Choose RPC when a service needs an immediate response — perfect for APIs or user data retrieval.

Example

A “new user signup” triggers Pub/Sub to notify email, billing, and analytics systems. The login flow, however, uses RPC to fetch user credentials in real time.

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Why Is It Important

Choosing between Pub/Sub and RPC impacts scalability, latency, and reliability. Pub/Sub scales better with loose coupling; RPC offers simplicity for direct, quick interactions.

Interview Tips

Explain the difference using coupling and timing: Pub/Sub = asynchronous and loosely coupled; RPC = synchronous and tightly coupled. Back your answer with real-world examples.

Trade-offs

Pub/Sub trades immediacy for scalability and decoupling, while RPC provides speed but risks tight coupling and failures cascading across services.