windows azure web role not available while upgrading

I am doing an automatic upgrade through Azure portal. While it is upgrading 1st instance, if I try to access my site through http://xyz.cloudapp.net it doesn't open.

IMO when 1st instance is upgrading, the request should be served from the 2nd instance, but I think this is not happening, that's why I see site unavailable message 开发者_如何学Pythonon my browser.

Is it something which I need to do/configure before I do an upgrade?

Your understanding matches mine. I would open a support ticket (http://windowsazure.com/support) to get to the bottom of it.

You want to handle the RoleEnvironmentChanging event properly (i.e. don't set the e.Cancel to true if you don't need to reboot)

http://msdn.microsoft.com/en-us/library/gg432963.aspx