Load Distribution

Getting a faster machine and connection is almost always enough.
Enterprise Java Beans (EJB) are designed to be distributable objects. As such, an EJB must follow certain rules.
Servlets have no such rules, but a good approximation is
1. Instance and static variables should not store state, since different instances of the servlet might exist.
2. ServletContext cannot be use to store state, for the same reason.
3. Any object placed in HttpSession should implement java.io.Serializable.
4. Use the getServletContext()getResource() to read files.
If you follow these rules you can mark servlet as <distributable/> in web.xml
There are several distribution (clustering) styles.
1. No clustering.
2. Clustering with no session migration and no session failover. Sessions stick to original server. A crash can result in broken session.
3. Clustering with session migration and no session failover. All session objects must be serializable.
4. Clustering with session migration and failover. Crash does not invalidate session.
These are implemented by servlet server. You must simply follow the rules.