The fundamental request flow pattern in distributed systems.

Understanding the basic request flow is fundamental to every distributed system design. The diagram below illustrates the common path a request takes from client to server and back, touching load balancing, service processing, data storage, and caching layers.

Request Flow Diagram

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What to Observe

1. Client → Load Balancer — The request enters through a load balancer that distributes traffic across service instances.
2. Load Balancer → Service — The selected service instance picks up the request for processing.
3. Service → Cache — Before hitting the database, the service checks the cache for frequently accessed data.
4. Service → Database — On a cache miss, the service queries the database and optionally populates the cache for future requests.
5. Response Path — The response travels back through the same layers to the client.

Key Takeaways

• Every additional network hop adds latency — minimize them where possible
• Caching dramatically reduces database load for read-heavy workloads
• Load balancers enable horizontal scaling by adding more service instances
• This basic pattern applies to the majority of system design interview questions