Client-Server Communication Patterns

A client that wants new data can ask for it, or the other side can tell it, and the five common patterns differ in who starts and what stays open between messages. The topic opens on a map of all five, then gives each one the same treatment: who starts, the messages in order, what it costs the server, and when it fits. A comparison turns direction and frequency into a choice, and a gotcha shows what happens to a webhook while your endpoint is down, using two real senders that behave differently. Practice applies the choice to four features.