Occurs before a simultaneous change to the service configuration is applied to the running instances of a role. A simultaneous change affects all role instances at the same time.
Microsoft.WindowsAzure.ServiceRuntime (in Microsoft.WindowsAzure.ServiceRuntime.dll)
Public Shared Event SimultaneousChanging As EventHandler(Of SimultaneousChangingEventArgs)
The SimultaneousChanging event and the SimultaneousChanged event are used together to identify and manage configuration changes to the service model that are seen by all role instances at the same time. You cannot cancel the SimultaneousChanging event and the role will not restart when this event is received.
You can configure your application to receive simultaneous notifications about role configuration changes by setting the value of the topologyChangeDiscovery attribute to Blast in the service definition file. When the SimultaneousChanging event is received, the role instance has to accept the change. For more information about settings in the service definition file, see Windows Azure Service Definition Schema.
The following code example shows how to use the SimultaneousChangingEventArgs object to obtain notification of simultaneous topology changes that are being made to the role:
public override bool OnStart()
private void RoleEnvironmentSimultaneousChanging(object sender,
// Get the list of topology changes
var topologyChanges = e.Changes.OfType<SimultaneousTopologyChange>();
foreach (var change in topologyChanges)
// Code to process topology changes for the role instance
This event occurs after the change has been submitted, but before the changes have been applied to each running role instance.
Windows Vista, Windows 7, Windows Server 2008, Windows 8.1, Windows Server 2012 R2, Windows 8 and Windows Server 2012