A COM+ QC application that you also configured to run as a Windows NT service is the only COM server configuration that you can cluster (889474)

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The only type of COM server that you can cluster is a COM+ QC application that you also configured to run as a Windows NT service. Other clustered COM servers may not function correctly, and intermittent problems may occur. At least two problems are known to occur when you cluster COM servers.

Problem 1

The cluster service is not aware of COM activation. Therefore, when the cluster service starts a generic application cluster resource for COM server, the application does not start under the correct identity. The correct identity is specified in the identity property of the corresponding COM or COM+ application.

Solution 1

The cluster service is aware of how to properly start NT Services when using a generic service resource. Therefore, this problem does not occur on a COM server that you configured to run as a Windows NT service. The cluster service uses the Service Control Manager (SCM) to start the service. The SCM starts the service under the appropriate identity that is configured in the identity property of the service.

Note On computers that are running Microsoft Windows XP, you can configure a COM+ 1.5 application to run as a Windows NT service.

Problem 2

COM is not cluster-aware. Therefore, if the Remote Procedure Call Server Service (RPCSS) starts a COM server, RPCSS starts a nonclustered instance of the COM server. This behavior may occur if an administrator manually starts the COM application or if a COM object instantiation automatically starts the application. After the nonclustered COM server is running, a clustered instance that is started later by the cluster service may not start. Typically, this causes problems in failover scenarios. The failover scenarios are frequently difficult to reproduce or diagnose.

Solution 2

This problem does not occur if the COM server has startup code to end the startup of a nonclustered instance of the server. For COM+ QC applications, the COM server does not start if it cannot find the appropriate Microsoft Message Queuing (MSMQ) queue. For a COM+ QC application that is configured to use a queue on the local clustered Message Queuing instance, the COM+ QC application only finds the queue if a clustered instance of the COM+ application is started. Therefore, the COM server has built-in protection against starting a nonclustered instance of a COM+ QC application. Other COM and COM+ servers do not have this built-in protection.