I Built a Usage-Based Billing Engine From Scratch — Here's How It Works

The author built MeterFlow, a usage-based billing engine handling event ingestion, deduplication, aggregation, fraud detection, tiered pricing, and Stripe invoice generation using TypeScript, Fastify, Redis, ClickHouse, and MinIO. Redis SET NX provides atomic deduplication with a 30-day TTL, while ClickHouse handles analytics and aggregation, with the entire architecture designed to map to production AWS equivalents.