Message Queuing & Event-Driven Architecture Flashcards

Which messaging protocol is commonly used for lightweight, low-bandwidth IoT device integration and operates on a publish/subscribe model over TCP?

Answer: MQTT

MQTT (Message Queuing Telemetry Transport) was designed for constrained devices and low-bandwidth networks, using a pub/sub model with a small packet overhead ideal for IoT integration.

In event-driven architecture, what is an 'event schema registry' primarily used for?

Answer: Storing and enforcing versioned schemas to ensure producers and consumers agree on event structure

A schema registry (such as Confluent Schema Registry) stores Avro/JSON/Protobuf schemas and validates messages against them, preventing schema incompatibilities from breaking consumers.

What is 'back-pressure' in a message-driven integration pipeline?

Answer: A flow-control mechanism where a slow consumer signals the producer to slow down or pause to avoid being overwhelmed

Back-pressure is a signaling mechanism that allows a downstream component to inform upstream producers to reduce throughput, preventing memory exhaustion and cascading failures.

When designing a message-based integration, what does 'message TTL' (Time-To-Live) control?

Answer: How long a message remains in the queue before being discarded or moved to a dead letter queue if not consumed

TTL sets an expiry duration on messages so that stale, time-sensitive events (e.g., real-time stock prices) are automatically removed if not consumed within the acceptable time window.

Which pattern is best suited for integrating a legacy system that cannot be modified to publish events directly into a modern event-driven architecture?

Answer: Change Data Capture (CDC) from the legacy system's database transaction log

CDC reads the database transaction log (e.g., via Debezium) to detect changes without modifying the legacy application, converting database changes into events for the modern platform.

A system integrator is designing a workflow where multiple independent services each process the same order event. Which pattern best supports this requirement?

Answer: Choreography-based event fan-out where each service subscribes to the same topic

Choreography-based fan-out via pub/sub allows multiple independent services (inventory, billing, shipping) to each subscribe to and react to the same order event without tight coupling.

What is the primary difference between message queuing and event streaming platforms like Kafka?

Answer: Streaming platforms retain messages as an ordered, replayable log, while traditional queues typically delete messages after consumption

Unlike traditional queues that remove messages upon consumption, Kafka retains events in an ordered, immutable log for a configurable retention period, allowing consumers to replay from any offset.