I have an ASP.NET application that is running on two load balanced servers. Everything is working fine except for one group of customers. All of these customers are coming from the same company. Randomly, an unhandled NullReferenceException error is thrown. It happens at random times in random places. It seems as if the session is just totally gone. since this is only happening for a specific group of users I have to assume that is has something to do with thier environment. I have seen users coming in with IE6, IE7, IE8 and FF and it the error occurs in all cases.
I am not 100% sure how to troubleshoot this. Does anyone have any ideas?
EDIT: Session is set to “InProc”
<sessionState mode="InProc" cookieless="false" timeout="20" />
I got in contact with the user that was having the porblem. I asked him to open a browser and go to whatsmyip.org and tell me what it says is his IP address. Then I asked him to refresh the screen a few times. Well, wouldn’t you know it, the IP address changed. It kept switching between two different IP addresses. This was not the IP address of his machine but of two different proxies. Each request could come form one or the other apparently.
Our load balancer (something called Zeus – I am not a network guy) was set to estabilsh session affinity (a.k.a. sticky connections) using IP addresses. We changed the settings so that the load balancer would drop a cookie and use that to maintain the session and everything works correctly now.