Microservices should be well defined through service contracts. A service contract basically gives information about how to consume the service and what all the parameters are that need to be passed to that service. Swagger and AutoRest are some of the widely adopted frameworks for creating service contracts. Another salient characteristic is that nothing is stored and no state is maintained by the microservice. If there is a need to persist something, then it will be persisted in a cache database or some datastore.