Of course, you can't use the class diagram(directly). It, and only it is about OOP.
But all other diagrams are opened for use. For example:
- Data diagrams for your DB planning
- Communication, sequence, state machine and activity diagrams for cooperation of your servers and pages.
- Deployment for to plan where will lies what.
- Timing diagram - to resolve the timeouts.
- What is funny, you even can use the class diagrams - for planning UI for a page - every element on the page has its elements and its functions and I use the class diagram for it.