Stateless and Stateful

• Is state stored on the backend

• Parts of system can be stateless or stateful

• As a client must I go to specific server to process something

• Style of storing state in an app

  • and relying on the state being there, ow things will break

• Completely stateless systems are rare

  • State is carried with every request

  • ie JWT

What

• Stateful

  • Stores state about clients in its memory

  • Depends on the information being there

  • examples

    • caches attached to servers

    • cookies/sessions stored in memory in app

    • load balanced servers, may hit different server which does not know about your session (may have to log in again)

• Stateless

  • Client is responsible to “transfer the state” with every request

  • May store but can safely lose it

    • ie in a database/file

  • still store data somewhere else

  • Can you restart the backend during idle time while the client workflow continues to work?

  • the backend/app can be stateless, but the whole system can be stateful

  • Example

    • instead of storing sessions in app memory, store it in database, thus no matter what instance/replica of the server you go to, it can retrieve the session from the database

Protocols

• tcp -> stateful

  • maintains the message order etc, if this is lost the connection dies and needs to restart

• udp -> stateless

  • Can come from multiple servers

• DNS (is udp) -> stateless

• Can build stateless protocol over stateful one

  • http over tcp

    • if tcp connection dies, http will create another one

Issues