Non functional Requirement(NFR):

1. sizing estimatation of app: register user -> concurrent user -> active concurrent user

   • active concurrent user: one connection to http server and on thread of execution running in app server(1:10 of concurrent user, for OLTP On-Line Transation Processing,it is about 1:5)

   • inactive concurrent user 需要考量的有：

     • Number of concurrent users(session timeout setting)
     • Requests per second(CPU load)
     • Logons per second(CPU sizing of LDAP and DB)

2. Availability = MTBF/(MTBF+MTTR)

   • MTBF: Mean Time Between Failure
   • MTTR: Mean Time To Repaire