https://www.dotnetzone.gr:443/cs/blogs/pkefal/archive/2009/11/27/windows-azure-amp-ndash-what-is-an-upgrade-domain.aspxWindows Azure automatically divides your role instances into some “logical” domains called upgrade domains. During upgrade, Azure is updating these domains one by one. This is a by design behavior to avoid nasty situations. Some of the last feature additionselCommunityServer 2.1 SP3 (Build: 20423.1)