Broker Architecture

Imagine an order service whose code needs to call inventory.reserve(sku, 2). The inventory object does not live in the same process. It runs on another machine, and several copies of it may be running at once.

The caller knows what it wants done but does not know which specific server is currently available to do it, where that server is running, or how to reach it directly. Now multiply this by hundreds of services, each of which calls several others.

Without any coordination mechanism, every client must maintain its own registry of server addresses