At the start of the diagram, we included the service registry. This is a dynamic database maintained on the startup and shutdown events of all microservices. Services subscribe to the registry and listen for updates to know whether the service has gone down or not. The entire process is done through the service registry and discovery. The registrator updates the registry whenever a service goes down or goes up. This registry is cached on all clients who subscribe to the registry, so whenever a service needs to be interacted with, an address is fetched from this registry. We will look in detail at this process in Chapter 6, Service Registry and Discovery.