1. The Top 10 Anti-Patterns
1. Buzzword Bingo: Saying 'I will use Kafka and Cassandra' within 30 seconds before defining what data is being transmitted or queried.
2. Silent Thinking: Going quiet for 4 minutes while sketching. Interviews are collaborative conversations; verbalize your reasoning.
3. Skipping Non-Functional Requirements: Forgetting to clarify whether consistency matters more than availability.
4. Drawing Single Boxes Without Data Flow: Showing an arrow between two boxes without defining protocols (HTTP, gRPC, WebSocket).
5. Ignoring Scale Math: Sizing a database for 10 users instead of 100M users.
6. Treating Sharding as Magic: Claiming 'I will shard by User ID' without explaining how cross-partition queries will be resolved.
7. Forgetting Caching Invalidation: Adding Redis everywhere without considering stale data or cache stampedes.
8. Over-Engineering on Simple Prompts: Proposing a 10-node Kafka cluster for a system handling 2 requests per minute.
9. Defensive Reactions to Feedback: Arguing with the interviewer when they point out a bottleneck instead of exploring the trade-off.
10. Failing to Conclude: Running out of time without summarizing failure modes or trade-offs.
2. How to Turn Mistakes into Opportunities
When an interviewer challenges your choice of database, treat it as a dialogue: 'That is a fair concern; if read latency degrades due to table locks, we can introduce a read-replica pool or move hot queries to Redis. Let's compare both options.'
Model this architecture on the HLDForge Canvas
Turn static box diagrams into living, collaborative systems. Drag and drop microservices, Kafka clusters, and cache tiers. Run automated SPOF detection and STRIDE threat modeling in real time.
Written by HLDForge Architecture Team
Former FAANG Bar Raiser & Staff Architect
The HLDForge Architecture Team publishes practical engineering guides, real-world case studies, and high-concurrency blueprints to help engineers build scalable and fault-tolerant software.