In large scale and multi-server setup, the web application should be Distributable. This means that any client can access any server of the cluster, provided that the application is in a distributable state. Advantages of a distributable web application is that each session is recognized in each member of the cluster, and the client will not re-login if it is redirected to another server.
More detailed explanation of a distributable web application using tomcat is in the link below.
Also a side note on Servlet-Context is provided in the link below