Below is a diagram I did when I started learning about application servers. To me it was important to make the distinction between the web server, the application server and the EIS (Enterprise Information System) tier such as database servers, etc
The web server I’ve considered was Apache web server and the application server was Tomcat Servlet container. At the time I had very limited knowledge on the whole concept of an application server and firewalls.
Another diagram I did a few years later after understanding the concept of clustering and SSL