Managing upgrades and changes to a hosted service
Windows Azure instances and the Guest OS they reside in have to be upgraded occasionally. The hosted service may need a new software deployment or a configuration change. The Guest OS may need a patch or an upgrade to a new version. To ensure that a hosted service can remain online 24*7, Windows Azure provides an upgrade capability that allows upgrades to be performed without stopping the hosted service completely, as long as each role in the service has two or more instances.
Windows Azure supports two types of upgrade: in-place upgrade and Virtual IP (VIP) swap. An in-place upgrade applies changes to the configuration and code of existing virtual machines (VM) hosting instances of the hosted service. A VIP swap modifies the load-balancer configuration, so that the VIP address of the production deployment is pointed at the instances currently in the staging slot and the VIP address of the staging deployment is pointed at the instances currently...