What is session persistence?
Session persistence is a means of directing a client request(s) to the same, single backend server for the duration of that session. This kind of persistence is also referred to as a "sticky session".
A persistent session, where a user’s requests are directed to the same server throughout a transaction or session, ensures that transactions requiring multiple, related steps can be completed seamlessly because the client and server exchange data and store state information (context). Varnish solutions enable the flexibility to ensure that your web application can maintain state per session.