Please refer to this link for the general prpc architecture: https://docs-previous.pega.com/pega-72-platform-installation-guide-tomcat-and-postgresql. At high level, prpc requires an application server (e.g., tomcat) and a database server (e.g. postgresql). apache web server is optional, but normally setup in a production system to handle static content whereas dynamical content will be handled by application server such as tomcat.