Practice & Assessment
Test your understanding of Pub/Sub and Streams
Multiple Choice Questions
5A subscriber disconnects for 30 seconds. Using Redis Pub/Sub, how many messages sent during that time will it receive on reconnect?
What does XACK do in a Redis Stream consumer group?
Which XREADGROUP argument means 'give me messages not yet delivered to any consumer in my group'?
What Redis config must you set to receive key expiry notifications via Pub/Sub?
Which messaging pattern guarantees each message is delivered to exactly one consumer?
Coding Challenges
1Real-Time Notification System
Build a simple notification system with two processes: a Publisher that sends a notification (userId, message, timestamp) to a Redis Pub/Sub channel notifications:<userId> every 2 seconds, and a Subscriber that listens on that channel, prints received messages, and stores them in a Redis Stream notifications:log using XADD. After 10 messages, read and print the full stream with XRANGE. Input: none (hardcoded userId). Output: console log of received notifications and stream contents. Estimated time: 25 minutes.
Mini Project
Event-Driven Order Processing Pipeline
Build a simulated order processing system using Redis Streams. Implement: an Order Service that writes order events (orderId, userId, items, total) to a Stream 'orders' using XADD. Create a consumer group 'processors' with two consumers: InventoryConsumer (reads orders, checks a Hash 'inventory:<productId>' for stock, writes to a result Stream 'inventory:results') and BillingConsumer (reads orders, simulates charging by writing to 'billing:results'). Both consumers XACK after processing. Add a monitor script that reads XPENDING every 5 seconds and XCLAIMs entries older than 10 seconds. Demonstrate failed processing by stopping one consumer mid-run and watching the monitor reclaim its messages.