如何跨多台服务器管理用户会话？

Question

I have a web service which authenticates a user, and if successful gives them a JSON Web Token which they can use to persist their session.
Currently I only have one server, but would ideally like to increase that to two or more for the sake of performance, however I'm unsure as to how that'll work with different servers as they'll have different instances of maintaining who is currently logged in.

For example, my service will examine the JWT the client returns, and (assuming it's a good token), will take the user ID and session and check if there is a user logged in with that session ID.
However, if for example, the middleware that precedes the web service layer determines that the server the user was initially logged in is currently unavailable and routes the request to a different server instance of the web service, how is the authentication controller meant to evaluate if the request is valid?

A very basic version of my service can be found below, with the black arrows representing ordinary communication, and the red arrows representing communication in the event that Layer One decides to route the request to Instance Two. Layer One, in essence is very basic and doesn't really do anything other than route traffic to the next layer dependent on the availability of the layer two instances.

Answer 1

One of the main advantages of JWT is that it does not need server storage because it is self-contained and stateless. If you need server sessions may be JWT it is not your best option to manage authentication. See Stop using JWT for sessions

Currently application servers use the SESSION ID to manage load balancing and redirection to the server that store the user session, including persistent storage and migration of session. Using a JWT you won't take profit of these characteristics.

Use JWT if you need a REST stateless endpoint with authentication or you need to exchange data securely between parties