CSI Message Queuing & Event-Driven Architecture 2 — Questions and Answers
Question 1: In RabbitMQ, which exchange type routes messages to queues based on an exact match of the message's routing key?
- Fanout exchange
- Topic exchange
- Direct exchange (Correct answer)
- Headers exchange
Correct answer: Direct exchange
A direct exchange routes messages to queues whose binding key exactly matches the message's routing key, making it suitable for task distribution to specific workers.
Question 2: What is the CQRS pattern and how does it relate to event-driven architectures?
- Command Query Responsibility Segregation — separates read and write models, often using events to sync the write side to read projections (Correct answer)
- Centralized Queue Routing System — a central broker pattern for managing event streams
- Concurrent Query and Response System — a method for parallel event processing
- Cross-Queue Replication Scheme — a redundancy pattern for message queues
Correct answer: Command Query Responsibility Segregation — separates read and write models, often using events to sync the write side to read projections
CQRS separates command (write) and query (read) operations, and pairs naturally with event sourcing: commands emit events that update denormalized read models asynchronously.
Question 3: A system integrator needs to guarantee message ordering within a specific subset of events. Which Kafka feature supports this requirement?
- Consumer group rebalancing
- Topic compaction
- Partition keying by a consistent message attribute (Correct answer)
- Broker replication factor
Correct answer: Partition keying by a consistent message attribute
By assigning a consistent partition key (e.g., customer ID), all messages with the same key are routed to the same partition, preserving order for that key within Kafka's ordered partition log.
Question 4: Which integration pattern uses a persistent store to record outgoing messages before they are sent, ensuring they are eventually delivered even if the broker is temporarily unavailable?
- Circuit breaker pattern
- Transactional outbox pattern (Correct answer)
- Saga orchestration pattern
- Competing consumers pattern
Correct answer: Transactional outbox pattern
The transactional outbox pattern writes the message to a local database table within the same transaction as the business operation, then a relay process publishes it to the broker, preventing message loss.
Question 5: In event-driven microservices, what is a 'saga' pattern used for?
- Compressing event payloads for efficient network transmission
- Managing distributed transactions across multiple services using a sequence of local transactions and compensating events (Correct answer)
- Scheduling periodic batch event generation
- Encrypting event streams between producers and consumers
Correct answer: Managing distributed transactions across multiple services using a sequence of local transactions and compensating events
The saga pattern coordinates multi-step distributed transactions by chaining local transactions and using compensating transactions to roll back completed steps if a later step fails.
Question 6: What does 'consumer group' mean in the context of Apache Kafka?
- A set of producers that share a common schema registry
- A named group of consumers where each partition is consumed by only one member, enabling parallel load-balanced processing (Correct answer)
- A cluster of Kafka brokers that replicate partitions
- A collection of topics grouped by business domain
Correct answer: A named group of consumers where each partition is consumed by only one member, enabling parallel load-balanced processing
A consumer group allows multiple consumer instances to share the work of consuming a topic, with each partition assigned to exactly one consumer in the group at a time for balanced parallel processing.
Question 7: Which of the following is a key characteristic of an idempotent consumer in a message-driven system?
- It acknowledges messages without processing them
- Processing the same message multiple times produces the same outcome as processing it once (Correct answer)
- It only processes messages during off-peak hours
- It transforms messages into a canonical format before storing
Correct answer: Processing the same message multiple times produces the same outcome as processing it once
An idempotent consumer handles at-least-once delivery safely by ensuring that reprocessing a duplicate message does not cause unintended side effects like double charges or duplicate records.
CSI Message Queuing & Event-Driven Architecture 2
In RabbitMQ, which exchange type routes messages to queues based on an exact match of the message's routing key?