Message Queue

Message Queues (Kafka, RabbitMQ, SQS)

Message queues let one service hand work to another without waiting, smoothing traffic spikes, decoupling services, and surviving downstream outages. This lesson covers the two queue families (broker-based like RabbitMQ and SQS vs log-based like Kafka), the delivery semantics (at-most-once, at-least-once, exactly-once), the operational essentials (DLQs, consumer groups, backpressure, ordering), and the trade-offs that decide between Kafka, RabbitMQ, and SQS for any given workload. By the end you can pick a queue and defend the choice with the per-property reasoning interviewers reward.

Event-Driven Architecture & Pub/Sub

Event-driven architecture (EDA) is a style where services communicate by emitting and reacting to immutable events instead of calling each other directly. This lesson covers the publish/subscribe pattern, the difference between event notification and event-carried state transfer, the role of an event bus, and how EDA reshapes coupling, scalability, and consistency. We compare it with request/response, walk through real implementations on Kafka, Kinesis, EventBridge, and SNS, and end with the operational pitfalls (event versioning, ordering, schema drift, observability) that bite teams who adopt EDA without preparation.