Today we are introducing a new upgrade mechanism, called “in-place upgrade,” which enables you to incrementally roll a new version of your service over the existing version without first deploying the new version to staging. With this new mechanism, you can upgrade your entire application or just a single role (e.g. web role) without disturbing the other roles in your application. Note that you will still have the option to upgrade as before, by first deploying the new version to staging and then swapping it with the production deployment.
To ensure application availability during an in-place upgrade, Windows Azure stops only a subset of your instances at a time to upgrade them, while keeping the remaining instances running. To achieve this, Windows Azure logically partitions your application into “upgrade domains” and updates one domain at a time. During the Community Technology Preview, Windows Azure uses two upgrade domains for each application. This means that half of your role instances will be offline at a time during an in-place upgrade. In the future, you will be able to choose how many upgrade domains you want.
You can perform in-place upgrades using the Windows Azure Portal or the new Service Management API. Note that you cannot use an in-place upgrade when the upgrade involves changes to your service definition (e.g., new roles or endpoints). For further details please refer to the MSDN documentation.
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