Practice
1. In a system designed for 99.999% availability, at step 4 the Delivery Worker checks the message queue for pending retries. What happens if the message is not acknowledged by the consumer within the visibility timeout?
easy
Solution
Step 1: Trace Delivery Worker decision at Step 4 -- message visibility timeout
If the message is not acknowledged within the visibility timeout, it becomes visible again for redelivery to ensure no message loss.Step 2: Eliminate incorrect options
Immediate deletion (A) risks message loss; archiving without retry (C) breaks availability; blocking (D) reduces throughput and availability.Final Answer:
Option C -> Option CQuick Check:
Visibility timeout expiry -> message re-queued for retry [check]
Hint: Visibility timeout expiry -> message re-queued for retry [check]
Common Mistakes:
2. A real-time leaderboard system must handle millions of score updates per second with low latency and provide instant rank queries. Which component is best suited to store and update scores efficiently while maintaining sorted order?
easy
Solution
Step 1: Identify data structure for sorted order and fast updates
Redis Sorted Sets provide O(log N) insertion and rank queries with in-memory speed, ideal for real-time leaderboards.Step 2: Eliminate other options based on latency and ordering
Relational DBs have higher write latency and complex locking; Kafka stores events but doesn't maintain sorted order; MongoDB lacks efficient sorted queries at scale.Final Answer:
Option D -> Option DQuick Check:
Redis Sorted Sets maintain sorted scores with low latency [check]
Hint: Sorted Sets keep scores sorted with fast rank queries [check]
Common Mistakes:
3. For an API Gateway that must support both REST and gRPC clients, which architecture best balances protocol support and transformation complexity?
medium
Solution
Step 1: Analyze protocol support requirements
Supporting both REST and gRPC clients in one gateway reduces operational complexity and centralizes transformation logic.Step 2: Evaluate alternatives
Use separate API Gateways for REST and gRPC, each optimized for its protocol increases deployment and maintenance overhead. Use REST-only API Gateway and require gRPC clients to use a proxy converting gRPC to REST adds latency and complexity on client side. Use gRPC-only API Gateway and require REST clients to upgrade to gRPC is impractical as REST clients are widespread.Final Answer:
Option D -> Option DQuick Check:
Single gateway with protocol translation balances support and complexity [check]
Hint: One gateway handles both protocols with internal translation [check]
Common Mistakes:
4. For a high-traffic API, which approach better captures user experience degradation under load: reporting average latency or reporting P95 latency, and why?
medium
Solution
Step 1: Understand average latency limitations
Average latency can be skewed by many fast requests and hide slow request impact, thus missing user experience degradation.Step 2: Why P95 latency is better
P95 latency captures the slowest 5% of requests, which often cause user frustration and indicate performance issues under load.Final Answer:
Option A -> Option AQuick Check:
P95 latency reveals slow requests impacting users better than average [check]
Hint: P95 reveals slow requests; average hides tail latency [OK]
Common Mistakes:
5. For a system requiring cost optimization with infrequent data access but occasional retrieval within hours, which storage architecture is preferable?
medium
Solution
Step 1: Analyze access and cost requirements
Data is infrequently accessed but needs retrieval within hours, so cold storage alone is too slow.Step 2: Evaluate tiering benefits
Warm storage offers moderate cost and latency; cold storage reduces cost further. Tiering balances cost and retrieval time.Final Answer:
Option A -> Option AQuick Check:
Warm + cold tiering balances cost and retrieval latency [check]
Hint: Warm + cold tiering balances cost and latency [check]
Common Mistakes: