HSPcomplete is using two Apache daemons: frontend and backend.
Frontend daemon serves static content (like images, CSS, JS etc.) while backend generates dynamic pages content and handles all of the business logics. Since Apache running HSPcomplete consumes a lot of memory, splitting it into two parts allows you to significantly optimize resource usage by running less backend Apache processes and more frontend processes.
"Server is under maintenance"
appears when backend apache daemon is stopped.
is a config file for Apache backend,
is a config file for Apache frontend;
is not used by HSPcomplete.