Client Side Discovery

Services typically need to call one another. In a monolithic, services invoke one another through direct calls. In a traditional distributed system deployment, services run at fixed, well known locations (host, port, etc) and can easily call one another using HTTP/REST or some RPC mechanism. A modern microservice based application typically runs in a virtualized or containerized environment where the number of instances of a service and their locations change dynamically. As a consequence of this, you must implement a mechanism that enables clients of services to make requests to a dynamically changing set of service instances.

To overcome this the client obtains the location of a service instance by querying a Service Registry which knows the locations of all service instances.

Disadvantage of this approach is that it couples the client to the service registry and client side service discovery logic needs to be implemented for each language/framework used within the client.