Introduction # A High Concurrency flash sale system is a system that is designed to handle a large number of concurrent users who are trying to purchase a limited number of items in a short period of time.
Imagine a small app where each client talks directly to a specific server, say https://10.0.0.1:8080. As traffic grows, that one server becomes a bottleneck, and if it crashes, the whole app is effectively down for any client pointing at it.
Modern APIs frequently access databases, or complex business logic that introduce significant latency and consume CPU and I/O resources. Without caching, every request pays the full cost of database queries, network calls, and computation. This can lead to slow response times and poor scalability as traffic increases.
Introduction # Distributed message brokers are the backbone of modern microservices architectures, enabling asynchronous communication, decoupling services, and providing a reliable way to handle data streams at scale.
Life Without a Rate Limiter # Imagine a public web API that allows clients to fetch user data without any rate limiting. Under normal conditions this might work, but during traffic spikes or abuse (e.g., bots or scrapers) the backend can be overwhelmed, leading to resource exhaustion, cascading failures, and poor availability for legitimate users. Without any form of control, a single noisy neighbor can starve others, increase infrastructure costs, and make it difficult to meet SLAs.
Every great architecture starts simple. But as we scale from a single monolith to a swarm of microservices, we hit a wall that only one pattern can break: the API Gateway. Phase 1: The Blissful Monolith # You have one server, one database, and one endpoint. Everything is easy:
