Great APIs start with contracts. Define your OpenAPI spec first, then scaffold handlers and validation from the schema to keep clients and servers in sync.
Defend your service with rate limiting, request timeouts, and input validation at the edge. Use a shared error format so consumers can react predictably.
Scale horizontally by keeping handlers stateless and pushing coordination to queues (e.g., RabbitMQ) and caches (e.g., Redis). Instrument every endpoint with latency, error rate, and saturation metrics.