If the only thing you want to be able to mark users online - I would do this -> whenever the user does something, update its "last_seen_time" to DateTime.Now I

If the only thing you want to be able to mark users online - I would do this -> whenever the user does something, update its "last_seen_time" to DateTime.Now If a user doesn't do anything for lets say, 5 minutes, you can mark it as offline.