How file rendering work in SharePoint using Office Web Apps server.
1. Client / User send request for File to HOST server that is our SharePoint server.
2. SharePoint server (HOST) Authentication of user using Claims authentication methods and creates auth_token for user and rights applied for file.
3. Then SharePoint Server (HOST) responds to client / User with WOPI Host page and iFrame for file from WOPI App.
4. Client / User Request for file from WOPI App to be displayed in the browser.
5. Then WOPI App Cache is checked for file existence. If file available in Cache then it Office Web Apps server respond with file.
6. In case file is not in Cache the WOPI (Office App server) existence is discovered perform checksum on file at WOPI Host or request File is not in cache
7. SharePoint Server (HOST) verify that request comes from Bound App server and then request file from Storage (file database).
8. Then Database server returns file from storage and sent it to host.
9. Later SharePoint server (HOST) Send file to WOPI App Server.
10. WOPI App server checks Cache file, generate rendering in Hot Blob Storage
11. WOPI App Send rendering of pages to Client.