The same principles that we discussed for classes can be mapped to higher-level concepts, for instance, microservices.
What does a stateful service look like? Let's take FTP as an example. If it's not anonymous, it requires the user to pass a username and password to create a session. The server stores this data to identify the user as still connected, so it's constantly storing state. Each time the user changes the working directory, the state gets updated. Each change done by the user is reflected as a change of state, even when they disconnect. Having a stateful service means that depending on the state, you can be returned different results for two identically looking GET requests. If the server loses the state, your requests can even stop processing correctly.
Stateful services can also have issues with incomplete sessions or unfinished transactions and added complexity. How long should you keep the sessions open? How can you verify...
