https://outhanchazima.dev/blog Engineering notes on system design, distributed systems and applied AI. en https://outhanchazima.dev/blog/design-patterns-for-multi-provider-payment-apis https://outhanchazima.dev/blog/design-patterns-for-multi-provider-payment-apis Sun, 07 Jun 2026 00:00:00 GMT How to integrate M-Pesa, Stripe (US & UK) and Paystack behind one clean interface using the Adapter, Registry and Facade patterns — with TypeScript examples, diagrams, the bad code to avoid, and what bad design costs the business in delivery speed and dollars. System Design Design Patterns Payments TypeScript APIs https://outhanchazima.dev/blog/designing-idempotent-payment-apis https://outhanchazima.dev/blog/designing-idempotent-payment-apis Mon, 18 May 2026 00:00:00 GMT A practical guide to exactly-once payment semantics — idempotency keys, request fingerprints, and the database patterns that make retries safe. Payments Distributed Systems APIs https://outhanchazima.dev/blog/event-driven-architecture-lessons https://outhanchazima.dev/blog/event-driven-architecture-lessons Thu, 02 Apr 2026 00:00:00 GMT Hard-won lessons on Kafka, eventual consistency, idempotent consumers, and observability from building event-driven platforms at scale. Event-Driven Architecture Kafka Distributed Systems