Scheduled MS Cluster Failovers using Automation Server Objects

Microsoft's Cluster Automation Server Objects enable developers and DBA's to manage their MS Cluster server through Component Object Model (COM) objects using COM aware languages such as Visual Basic and C++ and aware scripting languages like VB Script. In this article we will use Visual Basic 6.0 to develop a short application that can be scheduled to failover a server cluster. This article assumes that you are familiar with creating and running projects in Visual Basic and therefore skips basic things like variable declaration in an effort to keep the sample code blocks lean.

To develop code using the Cluster Automation Server objects you will need to download The Platform SDK if you do not already have it installed locally. At the time of this writing it can be downloaded from Microsoft at http://www.microsoft.com/msdownload/platformsdk/sdkupdate/psdk-full.htm.

To start, make a new "Standard.exe" project in Visual basic and add a reference in your Project references to "Microsoft Cluster Service Automation Classes.", msclus.dll.

Next, copy the code below and paste it into your project - the Form_Load method is fine. Modify the code to fit your environment:

'Create your cluster object 
Set oCluster = New Cluster 

'Open your connection, below change to name of your cluster
oCluster.Open ("MyCluster") 

'Hook into Resource Groups collection 
Set oClusGroups = oCluster.ResourceGroups 

'Retrieve a specific group, change below to name of the group you want to work with 
Set oClusGroup = oClusGroups.Item("My Cluster Group") 

Now you are hooked into your Cluster and a specific resource group. Next, determine your Active node:

'Determine the Active node 
sActiveNode = oClusGroup.OwnerNode.Name 

By knowing the Active node in a simple Active/Passive - 2 server configuration you can easily determine which node is passive. Let's skip that If Then statement and assume we assigned our passive node's name to a new string variable called sPassiveNode.

At this point, we have our cluster server objects all set up and know which server is active and which is passive. We are almost ready to failover. But before we failover it would be a good idea to make sure that the secondary node is healthy:

Set oSecondaryNode = oCluster.Nodes.Item(sPassiveNode) 
Dim bOkay As Boolean 
bOkay = True 


For i = 1 To oSecondaryNode.NetInterfaces.Count 
	If Not oSecondaryNode.NetInterfaces.Item(i).State = ClusterNetInterfaceUp Then 
		bOkay = False 
	End If 
Next 

If everything is fine on the passive node we will initiate failover. The "Move" method used below moves a group and it's resources from the current active node to another node. If no other node is specified it chooses a "preferred" node based on it's own predefined criteria. Since we are only using 2 nodes in our example we leave out the optional cluster Node parameter, but still pass in our Timeout parameter of 180 seconds.

If bOkay Then 
	varReturn = oClusGroup.Move(180) 
End IF 

'the move statement returns a variant that lets us know if the method timed out 
If CBool(varReturn) Then 
	Debug.Print ("Failover timed out") 
End If 

Summary