Charity Donation AppHigh-volume charity donation platform using Stripe PaymentIntent, internal donation intents, RabbitMQ, reconciliation worker, and Redis stats cache, designed to safely process 10M+ donations in a 3-day event with strong idempotency guarantees.Cache Strategy in System DesignAn experienced engineer’s walkthrough — who owns the cache, Cache-Aside vs Read/Write-Through vs Write-Behind, layering, and failure modes.Feed System BasicsAn experienced engineer’s walkthrough — pull vs push vs hybrid, why celebrities break push, and when to use each pattern.File Upload - Presigned URLAn experienced engineer’s walkthrough — why proxy upload hurts at scale, how presigned URLs work step by step, security, and when to use them.Metrics & Monitoring SystemAn experienced engineer’s walkthrough — metric types, collection, storage, alerting, and SLI/SLO.Notification System BasicsAn experienced engineer’s walkthrough — why to decouple notifications, event-driven flow, routing, channels, and failure handling.Payment IdempotencyAn experienced engineer’s walkthrough — why double charge happens, idempotency key, state machine, and reconciliation.Rate Limiter DesignAn experienced engineer’s walkthrough — why rate limiting is non-negotiable, where to put it, which algorithm to choose, and how to implement it correctly.URL Shortener DesignA step-by-step walkthrough for backend engineers — why short URL systems are not trivial, two critical flows, capacity math, architecture, short code generation, and key trade-offs.Back to home