| When you are ready to start loading applications and services in a clustered environment, there are some extra steps you have to take beyond the standard installation and configuration provided by the application or service. As with a cluster volume, you will most likely need to cluster-enable the application or service. You might also have to make some changes to the Cluster object and the cluster nodes so that they can properly support the new application or service. Cluster Resource Applications When creating a resource for an NCS cluster, you need to be familiar with the following types of applications: Cluster-aware Cluster-aware applications are specifically designed to take advantage of a clustered environment. These applications and services recognize when they are running on a cluster. They will automatically tweak their internal settings to be more tolerant of communication lapses that occur in a clustered system. Cluster-naive Although you can cluster-enable any application, if it is not designed to recognize that it is running on a cluster, the application is referred to as cluster-naive. For a cluster-naive application or service, NCS does all the work to ensure that the resource is reloaded on another node if the assigned cluster node fails.
Many OES Linux services, and some third-party applications as well, are designed to take advantage of Novell Clustering Services when it is detected. For example: Apache Web Server and Tomcat Servlet Engine GroupWise (MTA, POA, GWIA, WebAccess) iFolder iManager iPrint Novell clients (Windows 98 and Windows XP/2000) NetStorage
As you can see from this list, you can leverage the advantages of clustering with many types of applications, thereby making your entire network more resilient to failures. Cluster-Enabling an Application You cluster-enable a service or application by creating a Cluster Resource object for it in eDirectory. To create a cluster resource for an application, complete the following steps: 1. | From within iManager, select the Cluster Options link, found under the Clusters category in the left navigation frame.
| 2. | In the right pane, use the Object Selector or Object Browser tools to locate your cluster object. After you select the cluster object, the current page will automatically reload.
| 3. | Select New from the Cluster Objects window.
| 4. | Specify Resource as the new object type, and then click Next.
| 5. | At the New Resource screen, supply the necessary information and click Finish.
- Resource Name Specify a name for the new cluster resource.
- (Optional) Template If a resource template already exists for the resource you are creating, use the Object Selector to locate and select the template.
- Online Resource After Create Select this check box to automatically make the service available after resource creation.
- Define Additional Properties Check this box so that you can set the Cluster Resource object properties, such as Load and Unload scripts, after it is created. This causes the Finish button to change to Next, and opens several additional screens to configure resource properties, just as if you were configuring an existing cluster resource through the properties of the resource.
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NOTE NCS includes resource templates for DHCP, DNS, Generic IP services, iFolder, iPrint, and Samba. The generic IP service template can be used when configuring certain server applications to run on your cluster. You can edit and customize any of the templates for your specific needs. New templates can also be created in the same manner as creating cluster resources.
The cluster resource includes a unique IP address, which lets it be migrated from node to node within the cluster, as necessary. Cluster resources are created for both cluster-aware and cluster-naive applications. Assign Nodes to the Cluster-Enabled Resource When you create a cluster-enabled resource, all nodes in the cluster are automatically assigned to the resource. The order of assignment is determined by the order in which the nodes appear in the Assigned Nodes list. To assign or unassign nodes, or to change the failover order for the resource, complete the following steps: 1. | From within iManager, select the Cluster Options link, found under the Clusters category in the left navigation frame.
| 2. | In the right pane, use the Object Selector or Object Browser tools to locate your cluster object. After you select the cluster object, the current page will automatically reload.
| 3. | Select the check box next to the resource whose start and failover modes you are changing. Then click the Properties link in the Cluster Objects window to access the properties of the cluster resource.
| 4. | Select the General tab.
| 5. | From the list of unassigned nodes, select the server you would like to assign the resource to. Click the right arrow to move the server to the Assigned Nodes list. This process should be repeated for all servers that should be assigned to the resource.
| 6. | Click the up and down arrows to adjust the failover order of the servers assigned to the resource. Click Apply or Finish to save your changes.
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The first server in the Nodes list will be the preferred node for the cluster-enabled resource. Failover will occur sequentially down the list. Configure Clustered Resource Policies After a resource has been cluster-enabled, you can configure the start, failover, and failback parameters. To do this, complete the following steps: 1. | From within iManager, select the Cluster Options link, found under the Clusters category in the left navigation frame.
| 2. | In the right pane, use the Object Selector or Object Browser tools to locate your cluster object. After you select the cluster object, the current page will automatically reload.
| 3. | Select the check box next to the resource whose start, failover, or failback modes you would like to edit. Then click the Properties link in the Cluster Objects window.
| 4. | Select the General tab, and configure the following options:
- Resource Follows Master Check this box if you want the resource to only run on the master node in the cluster. If the master node fails, the resource will fail over to whichever node becomes the master.
- Ignore Quorum Check this box if you don't want the cluster-wide timeout period and node number limit enforced. This makes sure the resource is launched immediately as soon as any server in the Assigned Nodes list is brought online. You can modify the quorum values from the Cluster Configuration page in iManager.
| 5. | Continue with the resource configuration by adjusting the following options:
- Start When this option is set to Auto, the resource will start automatically whenever the cluster is brought online. When this option is set to Manual, you must start the device after the cluster comes online. The default is Auto.
- Failover When this option is set to Auto, the resource will automatically move to the next server in the Assigned Nodes list if the node it is currently running on fails. When this option is set to Manual, you will intervene after a failure and reassign the resource to a functioning node. The default is Auto.
- Failback When this option is set to Auto, the cluster resource will migrate back to its preferred node when it comes back online. The preferred node is the first node listed in its Assigned Nodes table. When this option is set to Manual, the cluster resource will not fail back until you allow it to happen. When this option is set to Disable, the cluster resource will not fail back to its most preferred node when the most preferred node rejoins the cluster. The default is Disable.
| 6. | Click Apply to save the configuration changes.
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Adjusting these settings give you granular control over the behavior of your clustered resource. Migrating a Cluster Resource A node doesn't have to fail in order to migrate a resource from one node to another. To migrate a cluster resource, complete the following steps: 1. | From within iManager, select the Cluster Manager link, found under the Clusters category in the left navigation frame.
| 2. | In the right pane, use the Object Selector or Object Browser tools to locate your cluster object. After you select the cluster object, the current page will automatically reload.
| 3. | Select the check box next to the resource you would like to migrate to another node. Then click the Migrate link in the Cluster State View window.
| 4. | Select the server you would like to migrate the resource to and click OK to migrate the resource.
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NOTE If you click Offline instead of Migrate, the resource will be unloaded, and will not load again until it is manually reloaded into the cluster. If you need to modify the resource configuration, Offline lets you take the resource out of the cluster in order to do so. Cluster resources can't be modified while loaded or running in the cluster.
You might want to do this in order to perform some type of maintenance on one of the nodes or just to balance out the node workload if one is getting too busy. Configuring Load and Unload Scripts Load scripts are required for each resource or volume in your cluster. The load script specifies the commands to start the resource or mount the volume on a node. Unload scripts are used to ensure that when a resource is removed from a node, all modules and resources are properly cleaned up in the process. TIP Load and unload scripts are created automatically for disk pools when they are cluster-enabled. Because of this, you shouldn't have to mess with scripts for cluster-enabled volumes and pools.
To create a resource load or unload script, complete the following steps: 1. | From within iManager, select the Cluster Options link, found under the Clusters category in the left navigation frame.
| 2. | In the right pane, use the Object Selector or Object Browser tools to locate your cluster object. After you select the cluster object, the current page will automatically reload.
| 3. | Select the check box next to the resource you are creating or editing a load script for. Then click the Properties link in the Cluster Objects window to access the properties of the cluster resource.
| 4. | Select the Scripts tab. Select either the Load Script or the Unload Script link.
| 5. | Edit or add the necessary commands to the script to load or unload the resource on a node. Sample commands are as follows:
SAMBA_ROOT=/mnt/samba exit_on_error mount t reiserfs /var/smb $SAMBA_ROOT ignore_error del_secondary_ipaddress ipaddress/subnet
| 6. | Specify a timeout value. The timeout value determines how much time the script is given to complete. If the script does not complete within the specified time, the resource becomes comatose. The default is 600 seconds (10 minutes).
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Resource load scripts are simply Linux shell scripts. Therefore, you use the same commands in a load script that you would use to create any other Linux shell script file that runs from a server terminal. Applications and services will often include prebuilt startup scripts for loading and unloading application modules. You can use these as a template for creating load and unload scripts. Consult the application or service documentation for information on necessary load and unload commands. |
