Vaadin is a framework for building rich web applications. Vaadin features server-side architecture where all of the business logic is located on server and only presentation layer is located on client side. Server-side architecture can be advantage since session state is stored on server. Statefulness can also be a disadvantage since server is frequently contacted. Obviously, the big mystery is scalability which is the main „pros and cons“ Vaadin battle. The question is, is Vaadin capable of satisfying the needs of an application that requires thousand of concurrent active users.