backend-concept-questions

Backend Questions

API Design & Security

• What is API versioning?
• What are common API vulnerabilities?
• Difference between PUT vs PATCH
• How do you secure APIs?
• What is rate limiting?
• How do you prevent duplicate requests?
• What is SSL termination?

Database & Data

• What is covering index?
• What is N+1 query problem?
• What is isolation level?
• What is schema migration strategy?
• How do you handle schema evolution in distributed systems?
• What is soft delete vs hard delete?
• How do you handle replication lag?
• What happens when cache and DB are inconsistent?

Distributed Systems

• What is distributed lock?
• What is distributed transaction?
• What is Saga pattern?
• How do you handle partial failure in microservices?
• How do you ensure data consistency across services?
• What is service mesh?
• How do you design for multi-region systems?
• What is fan-out problem?

Performance & Scalability

• What is backpressure?
• What is buffering?
• How do you handle high traffic spikes?
• How do you design a system for high write throughput?
• What is gzip compression?
• How do you handle the hot key problem in Redis?
• How do you handle hot partitions in sharding?
• How do you design pagination at scale?
• What is keep-alive?
• What is connection pooling?
• DB is becoming bottleneck, what next?
• Your DB CPU is 100%. What do you do?

Operations & Reliability

• What is blue-green deployment?
• How do you design a system that supports rollback safely?
• What is graceful shutdown for Docker container?
• What are multi-stage Docker builds?
• What is observability?
• What are latency percentiles (p50, p95, p99)?
• How do you debug a production issue?
• Your system is slow under high load, how do you debug?
• How do you identify a slow API?
• What is circuit breaker?

Runtime & Concurrency

• Difference between process vs thread vs async (event loop)
• Explain blocking vs non-blocking I/O
• How do you handle race conditions?
• How does garbage collection impact performance?