8. Using the Cluster Application Wizard
You can use the Cluster
Application Wizard to prepare your cluster for introducing an
application. Part of the wizard's job is to create a virtual server for
the application: essentially, virtual servers are simple ways to address
a combination of resources for easy management. Virtual servers consist
of a distinct resource group, a non-DHCP IP address, and a network
name, as well as any other resources required by whatever application
you want to cluster.
Once the virtual server
has been created, you configure the path and directory of the
application you want to cluster and then set advanced properties and
failover/failback policies for the entire virtual server, automating the
failure recovery process.
Let's step through the Cluster Application Wizard and configure our own fault-tolerant application, Notepad:
From
within the Cluster Administrator console, select Configure Application
from the File menu. The Cluster Application Wizard will appear. Click
Next off of the introductory screen.
The Select or Create a Virtual Server page appears next, as shown in Figure 15. You can choose to create a new virtual server or select an existing one from the drop-down list box. Click Next to continue.
The Resource Group for the Virtual Server screen appears next, as shown in Figure 16.
Identify the resource group by either creating a new one or selecting
an existing one that will handle the resources needed by your
application. In this example, we'll continue to use an existing one—if
you elect to create a new one, the process is much like that described
in the previous section. Click Next to continue.
The Resource Group Name screen appears next, as shown in Figure 17.
This gives you an opportunity to verify the resource group selection
you made on the previous screen. Confirm the information, make any
necessary changes, and then click Next to continue.
The Virtual Server Access Information screen appears next, as shown in Figure 18.
Here you specify a dedicated, static IP address for communicating with
the new virtual server. Enter the name and IP address you like, and then
click Next.
The Advanced Properties for the New Virtual Server screen appears next, as shown in Figure 19.
On this screen, you can choose any element of the virtual server you've
just created and modify its advanced properties. Select the item, and
then click the Advanced Properties button to modify the properties.
Otherwise, click Next to continue.
The Create Application Cluster Resource screen appears next, as shown in Figure 20.
Windows needs to create a cluster resource to manage the fault
tolerance of the resources contained in your new virtual server. Go
ahead and allow Windows to create a cluster resource now by clicking the
first option and then clicking Next.
The Application Resource Type screen appears next, as shown in Figure 21.
Specify the resource type for your new application, and then click Next. For this example, I'll
just configure a Generic Application type resource.
The Application Resource Name and Description page appears next, as depicted in Figure 22.
Here, name the new resource and enter a friendly description, which is
used only for administrative purposes. Click the Advanced Properties
button to configure policies on application restart, dependencies on
resources, and possible owners of the application. Click Next when
you've finished.
The Generic Application Parameters screen appears next, as shown in Figure 23.
Enter the command that executes the application and the path in which
the application resides. Choose whether the application can be seen at
the cluster console using the Allow application to interact with desktop
screen, and then click Next.
The Registry Replication screen appears next, as shown in Figure 24.
Enter any registry keys that are required by the application. These
will be moved to the applicable active node automatically by the Cluster
Service in Windows. Click Next when you've finished.
The Completing the Cluster Application Wizard appears next. Confirm your choices on this screen, and then click Finish.
The
new virtual server and cluster resource then is created and is shown
within the Cluster Administrator console. When you bring the group
online, you'll notice that a Notepad window is opened in the background.
If you close Notepad, it will automatically relaunch itself. This is
the power of the cluster, demonstrated in a simple form, of course.
9. Configuring Failover and Failback
Once you have resources, groups, virtual servers, and applications configured in your cluster, you need to specify failover
and failback
policies so that upon a failure your cluster behaves as you want it to
behave. In this section, I'll detail how to configure each type of
policy.
Failover is configured automatically on a cluster with two or more nodes. Failback is not. |
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9.1. Failover
You can configure a
failover policy by right-clicking any group within the Cluster
Administrator console and selecting Properties from the pop-up context
menu. Once the properties sheet appears, navigate to the Failover tab. A
sample Failover tab for a group is shown in Figure 25.
On this tab, specify the
threshold, which is the maximum number of times this particular group is
allowed to fail over during a specific timeframe, as specified by the
period option. If there are more failovers than specified in the
threshold value, the group enters a failed state and the clustering
service won't attempt to bring it back to life.
Click OK when you've entered an appropriate value.
9.2. Failback
You also can configure a
failback policy by right-clicking any group within the Cluster
Administrator console and selecting Properties from the menu. Navigate
to the Failback tab, a sample of which is shown in Figure 26.
You
can set the option to prevent failback, meaning that when a failed node
that originally hosted the group returns to normal functionality, the
migrated group will not return and will remain on its new host. If you
decide to allow failback, you can choose how quickly the group will
return to its original host—either immediately, or between a certain
period of time.
