IntermediateTECHNICAL
Describe a backend system you designed for high availability and scalability. What architecture patterns, data storage choices, caching strategies, and failure modes did you consider and why?
Backend Developer
General

Sample Answer

I designed the backend for a customer notifications platform that handled about 30M events/day with strict SLA requirements (99.95% uptime, sub‑1s delivery for 95% of messages). We used a microservice architecture on Kubernetes: an API gateway, an ingestion service, a rules engine, and channel workers (email, SMS, push). Kafka acted as the backbone between services so spikes were buffered instead of crashing downstream systems. For storage, we used PostgreSQL for configuration and user preferences, and DynamoDB for high‑volume event logs that needed cheap, scalable writes. On caching, we put Redis in front of user preference lookups and saw DB reads drop by ~70%. For availability, each service had at least 3 replicas across zones, health checks, and circuit breakers via a service mesh. We ran chaos tests to simulate Kafka outages, partial zone failures, and downstream provider timeouts. Under a 3x traffic spike, the system stayed within SLA and error rates stayed below 0.5%.

Keywords

Microservice architecture with Kafka as the event backbone for decoupling and bufferingHybrid storage: relational for config, NoSQL for high-volume event dataRedis caching to offload the DB and improve latencyExplicitly designing for and testing failure modes (zone loss, provider failures, spikes)