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NOTE: CentOS Enterprise Linux is built from the Red Hat Enterprise Linux source code. Other than logo and name changes CentOS Enterprise Linux is compatible with the equivalent Red Hat version. This document applies equally to both Red Hat and CentOS Enterprise Linux.

3.6. Configuring a Failover Domain

A failover domain is a named subset of cluster members that are eligible to run a cluster service in the event of a system failure. A failover domain can have the following characteristics:

  • Unrestricted — Allows you to specify that a subset of members are preferred, but that a cluster service assigned to this domain can run on any available member.

  • Restricted — Allows you to restrict the members that can run a particular cluster service. If none of the members in a restricted failover domain are available, the cluster service cannot be started (either manually or by the cluster software).

  • Unordered — When a cluster service is assigned to an unordered failover domain, the member on which the cluster service runs is chosen from the available failover domain members with no priority ordering.

  • Ordered — Allows you to specify a preference order among the members of a failover domain. The member at the top of the list is the most preferred, followed by the second member in the list, and so on.

By default, failover domains are unrestricted and unordered.

In a cluster with several members, using a restricted failover domain can minimize the work to set up the cluster to run a cluster service (such as httpd, which requires you to set up the configuration identically on all members that run the cluster service). Instead of setting up the entire cluster to run the cluster service, you must set up only the members in the restricted failover domain that you associate with the cluster service.

Tip Tip

To implement the concept of a preferred member, create an unrestricted failover domain comprised of only one cluster member. By doing this, a cluster service runs on the preferred member; in the event of a failure, the cluster service fails over to any of the other members.

To add a failover domain to the cluster software configuration, follow these steps:

  1. Select the Failover Domains property and click the Create a Failover Domain button. The Failover Domain dialog box is displayed prompting you to create a name for the domain. Enter a name for the domain and click OK, which then displays the Failover Domain Configuration dialog.

  2. In the Failover Domain Configuration dialog box (shown in Figure 3-9), there are several options available to customize the failover domain for your resource and/or service.

    Figure 3-9. Configuring a Failover Domain

    Enter a name for the domain in the Domain Name field. The name should be descriptive enough to distinguish its purpose relative to other names used on your network.

  3. Click Available Cluster Nodes drop-down to select the members for this failover domain.

  4. Check Restrict Failover To This Domains Members to prevent any member other than those listed from taking over a cluster service assigned to this domain.

  5. Check Prioritized List if you want members to assume control of a failed cluster service in a particular order. Click the Adjust Priorities arrows to configure order of the nodes in the domain. Preference is indicated by the member's position in the list of members in the domain, with the most preferred member given the higher priority value.

  6. Click Close to create the domain.

  7. Choose File => Save to save the changes to the cluster configuration.

To remove a member from a failover domain, follow these steps:

  1. On the Failover Domains property, click the name of the domain you want to modify (or select the domain and click Edit Failover Domain Properties).

  2. In the Failover Domain Configuration dialog box, click the name of the member you want to remove from the domain and click Remover Member from Domain. (Members must be deleted one at a time.)

  3. When finished, click OK.

  4. Choose File => Save to save the changes to the cluster configuration.

  Published under the terms of the GNU General Public License Design by Interspire