Service Discovery Pattern

 Problem

When microservices come into the picture, we need to address a few issues in terms of calling services:

1. With container technology, IP addresses are dynamically allocated to the service instances. Every time the address changes, a consumer service can break and need manual changes.
2. Each service URL has to be remembered by the consumer and become tightly coupled.

So how does the consumer or router know all the available service instances and locations?

Solution

A service registry needs to be created which will keep the metadata of each producer service. A service instance should register to the registry when starting and should de-register when shutting down. The consumer or router should query the registry and find out the location of the service. The registry also needs to do a health check of the producer service to ensure that only working instances of the services are available to be consumed through it. There are two types of service discovery: client-side and server-side. An example of client-side discovery is Netflix Eureka and an example of server-side discovery is AWS ALB.