Hello, Server

§01The request/response cycle

A client (browser, mobile app, another service) sends a request over the network. A server receives it, does some work, and sends a response back. Until that response arrives, the request is in flight.

On the canvas, an edge from a client to a server represents that connection. When you press Run, you'll see dots travel along the edge in both directions: forward (the request) and return (the response).

§02Why this matters

• Every more-complex pattern (caches, queues, shards) is built on this primitive.
• Latency is measured end-to-end: client → server → client. Adding hops adds latency.
• If a server is down or unreachable, the request fails — the dot is dropped.

• Client → Server is the atom of every system you'll build.