We will start by converting the monolithic application that we have generated into a microservice gateway application.
Even though microservices are made up of different services inside, for end users it should be a single, unified product. There are a lot of services that are designed to work in a lot of different ways, but there should be a single entry point for users. Thus, we need a gateway application, since they form the frontend of your application.
Segregate the internal contracts and services from external users. We may have application-level internal services that we shouldn't expose to external users, so these can be masked away. This also adds another level of security to the application.
Easier to mock services for testing help validate the services independently in integration testing.