Backing services are addressable

All backing services should be accessible through an addressable URL. All services need to talk to some external resources during the life cycle of their execution. For example, they could be listening to or sending messages to a messaging system, sending an email, or persisting data to a database. All these services should be reachable through a URL without complex communication requirements:

In the microservices world, microservices can either talk to a messaging system to send or receive messages, or they can accept or send messages to another service API. In a regular case, these are either HTTP endpoints using REST and JSON or TCP or HTTP-based messaging endpoints.