Logs out and with every refresh though not using TempDataProvider?

Question

I've got an app built using asp.net mvc and deployed over 2 Amazon EC2 instances. I'm using forms authentication to authenticate users. I simply make a quick look up on the given username and password and if I found a match I set an authentication cookie, like so:

if(_repository.Login(username, password))
    FormsAuthentication.SetAuthCookie(username, false);

This works fine as long as the application on one machine, but, once I leveraged Amazon Elastic Load Balancing to deploy the site on two machines, the site behaves in a very weird way. When a user logs in, the site recognizes a logged in user, after a refresh or two, the site no longer see the user as a logged in user. If the user keeps refreshing again for some time, the app sees the user as a logged in user again, and this goes forever.
I'm aware that such a problem might occur if I'm storing SessionState inproc. I'm not using SessionState at all.

What am I missing here guys?

Ps: I've edited the session state to be stored on a state server [Though i'm not using neither sessions nor TempData anywhere on my app] and the same weird behavior is there.

Answer 1

You need to synchronize your <machinekey> between all servers in your farm. Otherwise the forms authentication ticket is only good for the machine which issued it. I doubt this has anything to do with Session/TempData.