I would like to know the number of users logged into my ASP.NET 2.0 application.
Points to be considered: 1) Simplest way would be to use Application or Cache object to have the counts on Session start or end. However this would fail if there is a worker process recycle. Wouldn't it?
2) Should't make a difference whether the session is inproc/state server managed/ or SQL server managed.
3) Should preferably be seamless to a web-farm architecture.
You should store a user's online status in a database. Each time a page is navigated, their LastActivity information (in the database table) is updated.
Create a SQL job that runs and logs users off if there is X amount of inactivity (and of course, if they actually do hit logout, update the database to mark the user offline)
ASP.Net comes with several performance counters
http://msdn.microsoft.com/en-us/library/fxk122b4.aspx
State Server Sessions Active The number of currently active user sessions. This counter is available only on the computer where the state server service (aspnet_state) is running.
Requests/Sec The number of requests executed per second. This represents the current throughput of the application. Under constant load, this number should remain within a certain range, barring other server work (such as garbage collection, cache cleanup thread, external server tools, and so on).
If you use the built-in ASP.NET membership provider, then there's the ever-so-handy Membership.GetNumberOfUsersOnline() method.
(Of course, it only works authenticated users...)