Webpage ping when active
The best way is to ping the server while the user is online. Using other methods such as the Channel API with GAE proves to be unreliable since you are not constantly sending a ping message but rather just sending a disconnect message. If the browser crashes, no disconnect message is sent.
I want a way for users to open this webpage, and whenever they are on that page, it updates the server that they are on the page. It should only work when the user is actually looking at the webpage (not inactive, like from switchings tabs). One way to do this which I have implemented is to keep pinging the server saying that I am alive. 
This however causes a lot of load on the server and client side. I am using Google App Engine and webapp2, and was wondering if anyone knows a better way to do this.