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I have a need for a stateful webservice in our organization. However, everywhere I read online says that building a stateful webservice is bad programming but nothing ever says why. I guess I don't understand what is so bad about it. I also don't really understand why they would give a work around to allow you to have state in a webservice.
So I guess that my question is, why is it bad programming to use a stateful webservice and why would it be allowed?
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One example of a stateful application is a stateful web service that stores client authentication data on the server, labeling clients as having a “connected” or “disconnected” state. It also stores information about previous requests from the same clients.
Stateful means the computer or program keeps track of the state of interaction, usually by setting values in a storage field designated for that purpose. Stateless means there is no record of previous interactions and each interaction request has to be handled based entirely on information that comes with it.
A. REST APIs are stateless because, rather than relying on the server remembering previous requests, REST applications require each request to contain all of the information necessary for the server to understand it. Storing session state on the server violates the REST architecture's stateless requirement.
Stored Data: If the webserver stores data in a backend manner and uses it to identify the user as an always-connected client, the service is Stateful. While in Stateless, the server does store data, but in a database to verify user/client whenever it needs to connect.
The whole purpose of a web service is to deliver a piece of functionality in one transaction in a way that is highly scalable. This means keeping things simple and atomic.
When you have to make multiple calls to perform the operation, you have a great potential of leaving transactions hanging. Is the client coming back? Are they done? How long should the transaction remain open? Did they crash? How should rollbacks be handled?
The answers to these questions could have a radical impact on the resources necessary to run your service. Which is why everyone recommends doing it all in one swoop.
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Here are some reasons I can think of:
The cost of maintaining state will have to be borne server side only - service consumers are rarely web browsers, so have no cookies. This brings down your server performance and increases your design complexity.
A service consumer is an intelligent program, rather than a dumb browser. As such the program will (almost always) maintain its own state. In other words, when you provide a service, your consumer will request precisely the data it wants. Maintaining state on the server becomes obsolete and unnecessary.
Transactions - a service is a dangling point in your system because its clients are mostly intelligent, and they decide when to inform you of changes in their state. This means that if you maintain state, you might have to wait between service calls to finish a transactional operation. And there's absolutely no guarantee the client will ever make that next service call.
There are a lot of reasons, but these are the ones I can think of off the top of my head :)
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