Architecture

A recommendation service goes down and takes the whole product page with it. That is not a recommendation outage – it is a design failure. Graceful degradation is building so that a dead dependency costs you a feature, not the whole system.

API versioning sounds like a URL-format debate, but the real problem is changing an API without breaking clients you do not control and cannot redeploy. What actually counts as a breaking change, and how to evolve an API for years without a v2.

There are only two hard things in computer science, the joke goes, and cache invalidation is one of them. The caching patterns worth knowing, the staleness each one accepts, and the stampede that takes down services when a hot key expires.

A service slows down, every client retries, and the retries become the load that finishes it off. How retry storms form, why jitter matters more than backoff, and why retry budgets beat per-request limits.

Silo, bridge, or pool? Compare multi-tenant data isolation models on blast radius, cost, and operational load. Learn PostgreSQL row-level security, safe tenant context propagation, noisy-neighbour control, and how to migrate between models later.

How idempotency keys turn at-least-once delivery into safe, exactly-once API behavior, with request fingerprinting, response replay, and concurrency handling in Java and SQL.

Production patterns for eventual consistency in event-driven microservices: outbox, idempotency, sagas, schema evolution, and staleness UX.

A pragmatic Spring Boot implementation of hexagonal architecture with primary and secondary ports, module layout, and testing strategies that scale.

Practical guide to implementing Event Sourcing and CQRS in production systems. Covers event stores, read projections, snapshots, and honest trade-off analysis.