Service Discovery Pattern: An Example

A registry that maps one service name to one address is a phone book with one number per person. It works until the service has more than one instance, which is the normal case.

This lesson builds a registry that holds a list of instances for each name. It expires the ones that go quiet and hands callers a healthy address. The code runs, so the expiry can be watched rather than described.

The Three Jobs

The registry does three things, and each one matters on its own.

1. Registration: an instance says it exists, and says so again at intervals. 2