stateless protocol and stateful protocol
How to understand stateless protocol and stateful protocol? HTTP is a stateless protocol and FTP is a stateful protocol. For the web applications requiring a lot of interactions, the underlying protocol should be stateful ones. Is my understanding right?
Answer
HTTP is a stateless protocol, in other word the server will forget everything related to client/browser state. Although web applications have made it virtually look like stateful.
A stateless protocol can be forced to behave as if it were stateful. This can be accomplished if the server sends the state to the client, and if the client to sends it back again to the server, every time.
There are three ways this may be accomplished in HTTP:
a) One is cookies, in which case the state is sent and returned in HTTP headers.
b) The second is URL extension, in which case the state is sent as part of the URL as response.
c) The third is "hidden form fields", in which the state is sent to the client as part of the response, and returned to the server as part of a form's hidden data
SCALABILITY AND HIGH AVAILABILITY
One of the major reasons why HTTP scales so well is its Statelessness. Stateless protocol eases the replication concerns, as the state itself doesn't need to be stored on the server.
Stateful protocols are logically heavy to implement in Internet reliably. Stateless servers are also easily scalable, while for stateful servers scalablity is problematic. Stateless request can be sent to any node, at any time, while with Stateful this is not a case.
HTTP as Stateless protocol increases availability for stateless web applications, which otherwise would be difficult or impossible to implement. If there is connection lost, there is no state that is lost, simple request resend will resolve the problem. Stateless requests are also cacheable.