Architecting Modern Java EE Applications

Execute the app as one or more stateless processes

Ideally, applications run as stateless processes where every use case is executed self-sufficiently, without affecting other running processes. Potential state is either stored in an attached resource such as a database or discarded. Session state that lives longer than a single request is therefore a violation of this principle. The challenge with traditional user session state is that it only resides in a local application instance and not accessible from other instances. The need for so-called sticky sessions on load balancers is an indicator for not having a stateless application.

A lot of modern technology supports this approach. Docker containers with their copy-on-write file system ...