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Fence Configuration Guide

Chapter 4. Configuring Fencing with Conga

4.1. Configuring Fence Daemon Properties
4.2. Configuring Fence Devices
4.2.1. Creating a Fence Device
4.2.2. Modifying a Fence Device
4.2.3. Deleting a Fence Device
4.3. Configuring Fencing for Cluster Members
4.3.1. Configuring a Single Fence Device for a Node
4.3.2. Configuring a Backup Fence Device
4.3.3. Configuring a Node with Redundant Power
This chapter describes how to configure fencing in Red Hat High Availability Add-On using Conga.

Note

Conga is a graphical user interface that you can use to administer the Red Hat High Availability Add-On. Note, however, that in order to use this interface effectively you need to have a good and clear understanding of the underlying concepts. Learning about cluster configuration by exploring the available features in the user interface is not recommended, as it may result in a system that is not robust enough to keep all services running when components fail.

4.1. Configuring Fence Daemon Properties

Clicking on the Fence Daemon tab displays the Fence Daemon Properties page, which provides an interface for configuring Post Fail Delay and Post Join Delay. The values you configure for these parameters are general fencing properties for the cluster. To configure specific fence devices for the nodes of the cluster, use the Fence Devices menu item of the cluster display, as described in Section 4.2, "Configuring Fence Devices".
  • The Post Fail Delay parameter is the number of seconds the fence daemon (fenced) waits before fencing a node (a member of the fence domain) after the node has failed. The Post Fail Delay default value is 0. Its value may be varied to suit cluster and network performance.
  • The Post Join Delay parameter is the number of seconds the fence daemon (fenced) waits before fencing a node after the node joins the fence domain. The Post Join Delay default value is 6. A typical setting for Post Join Delay is between 20 and 30 seconds, but can vary according to cluster and network performance.
Enter the values required and click Apply for changes to take effect.

Note

For more information about Post Join Delay and Post Fail Delay, refer to the fenced(8) man page.

4.2. Configuring Fence Devices

Configuring fence devices consists of creating, updating, and deleting fence devices for the cluster. You must configure the fence devices in a cluster before you can configure fencing for the nodes in the cluster.
Creating a fence device consists of selecting a fence device type and entering parameters for that fence device (for example, name, IP address, login, and password). Updating a fence device consists of selecting an existing fence device and changing parameters for that fence device. Deleting a fence device consists of selecting an existing fence device and deleting it.
This section provides procedures for the following tasks:
From the cluster-specific page, you can configure fence devices for that cluster by clicking on Fence Devices along the top of the cluster display. This displays the fence devices for the cluster and displays the menu items for fence device configuration: Add and Delete. This is the starting point of each procedure described in the following sections.

Note

If this is an initial cluster configuration, no fence devices have been created, and therefore none are displayed.
Figure 4.1, "luci fence devices configuration page" shows the fence devices configuration screen before any fence devices have been created.
luci fence devices configuration page
The luci fence devices configuration page.

Figure 4.1. luci fence devices configuration page


4.2.1. Creating a Fence Device

To create a fence device, follow these steps:
  1. From the Fence Devices configuration page, click Add. Clicking Add displays the Add Fence Device (Instance) dialog box. From this dialog box, select the type of fence device to configure.
  2. Specify the information in the Add Fence Device (Instance) dialog box according to the type of fence device. In some cases you will need to specify additional node-specific parameters for the fence device when you configure fencing for the individual nodes.
  3. Click Submit.
After the fence device has been added, it appears on the Fence Devices configuration page.

4.2.2. Modifying a Fence Device

To modify a fence device, follow these steps:
  1. From the Fence Devices configuration page, click on the name of the fence device to modify. This displays the dialog box for that fence device, with the values that have been configured for the device.
  2. To modify the fence device, enter changes to the parameters displayed.
  3. Click Apply and wait for the configuration to be updated.

4.2.3. Deleting a Fence Device

Note

Fence devices that are in use cannot be deleted. To delete a fence device that a node is currently using, first update the node fence configuration for any node using the device and then delete the device.
To delete a fence device, follow these steps:
  1. From the Fence Devices configuration page, check the box to the left of the fence device or devices to select the devices to delete.
  2. Click Delete and wait for the configuration to be updated. A message appears indicating which devices are being deleted.
When the configuration has been updated, the deleted fence device no longer appears in the display.

4.3. Configuring Fencing for Cluster Members

Once you have completed the initial steps of creating a cluster and creating fence devices, you need to configure fencing for the cluster nodes. To configure fencing for the nodes after creating a new cluster and configuring the fencing devices for the cluster, follow the steps in this section. Note that you must configure fencing for each node in the cluster.
The following sections provide procedures for configuring a single fence device for a node, configuring a node with a backup fence device, and configuring a node with redundant power supplies:

4.3.1. Configuring a Single Fence Device for a Node

Use the following procedure to configure a node with a single fence device.
  1. From the cluster-specific page, you can configure fencing for the nodes in the cluster by clicking on Nodes along the top of the cluster display. This displays the nodes that constitute the cluster. This is also the default page that appears when you click on the cluster name beneath Manage Clusters from the menu on the left side of the luci Homebase page.
  2. Click on a node name. Clicking a link for a node causes a page to be displayed for that link showing how that node is configured.
    The node-specific page displays any services that are currently running on the node, as well as any failover domains of which this node is a member. You can modify an existing failover domain by clicking on its name.
  3. On the node-specific page, under Fence Devices, click Add Fence Method. This displays the Add Fence Method to Node dialog box.
  4. Enter a Method Name for the fencing method that you are configuring for this node. This is an arbitrary name that will be used by Red Hat High Availability Add-On; it is not the same as the DNS name for the device.
  5. Click Submit. This displays the node-specific screen that now displays the method you have just added under Fence Devices.
  6. Configure a fence instance for this method by clicking the Add Fence Instance button that appears beneath the fence method. This displays the Add Fence Device (Instance) drop-down menu from which you can select a fence device you have previously configured, as described in Section 4.2.1, "Creating a Fence Device".
  7. Select a fence device for this method. If this fence device requires that you configure node-specific parameters, the display shows the parameters to configure.

    Note

    For non-power fence methods (that is, SAN/storage fencing), Unfencing is selected by default on the node-specific parameters display. This ensures that a fenced node's access to storage is not re-enabled until the node has been rebooted. For information on unfencing a node, refer to the fence_node(8) man page.
  8. Click Submit. This returns you to the node-specific screen with the fence method and fence instance displayed.

4.3.2. Configuring a Backup Fence Device

You can define multiple fencing methods for a node. If fencing fails using the first method, the system will attempt to fence the node using the second method, followed by any additional methods you have configured.
Use the following procedure to configure a backup fence device for a node.
  1. Use the procedure provided in Section 4.3.1, "Configuring a Single Fence Device for a Node" to configure the primary fencing method for a node.
  2. Beneath the display of the primary method you defined, click Add Fence Method.
  3. Enter a name for the backup fencing method that you are configuring for this node and click Submit. This displays the node-specific screen that now displays the method you have just added, below the primary fence method.
  4. Configure a fence instance for this method by clicking Add Fence Instance. This displays a drop-down menu from which you can select a fence device you have previously configured, as described in Section 4.2.1, "Creating a Fence Device".
  5. Select a fence device for this method. If this fence device requires that you configure node-specific parameters, the display shows the parameters to configure.
  6. Click Submit. This returns you to the node-specific screen with the fence method and fence instance displayed.
You can continue to add fencing methods as needed. You can rearrange the order of fencing methods that will be used for this node by clicking on Move Up and Move Down.

4.3.3. Configuring a Node with Redundant Power

If your cluster is configured with redundant power supplies for your nodes, you must be sure to configure fencing so that your nodes fully shut down when they need to be fenced. If you configure each power supply as a separate fence method, each power supply will be fenced separately; the second power supply will allow the system to continue running when the first power supply is fenced and the system will not be fenced at all. To configure a system with dual power supplies, you must configure your fence devices so that both power supplies are shut off and the system is taken completely down. When configuring your system using Conga, this requires that you configure two instances within a single fencing method.
To configure fencing for a node with dual power supplies, follow the steps in this section.
  1. Before you can configure fencing for a node with redundant power, you must configure each of the power switches as a fence device for the cluster. For information on configuring fence devices, see Section 4.2, "Configuring Fence Devices".
  2. From the cluster-specific page, click on Nodes along the top of the cluster display. This displays the nodes that constitute the cluster. This is also the default page that appears when you click on the cluster name beneath Manage Clusters from the menu on the left side of the luci Homebase page.
  3. Click on a node name. Clicking a link for a node causes a page to be displayed for that link showing how that node is configured.
  4. On the node-specific page, click Add Fence Method.
  5. Enter a name for the fencing method that you are configuring for this node.
  6. Click Submit. This displays the node-specific screen that now displays the method you have just added under Fence Devices.
  7. Configure the first power supply as a fence instance for this method by clicking Add Fence Instance. This displays a drop-down menu from which you can select one of the power fencing devices you have previously configured, as described in Section 4.2.1, "Creating a Fence Device".
  8. Select one of the power fence devices for this method and enter the appropriate parameters for this device.
  9. Click Submit. This returns you to the node-specific screen with the fence method and fence instance displayed.
  10. Under the same fence method for which you have configured the first power fencing device, click Add Fence Instance. This displays a drop-down menu from which you can select the second power fencing devices you have previously configured, as described in Section 4.2.1, "Creating a Fence Device".
  11. Select the second of the power fence devices for this method and enter the appropriate parameters for this device.
  12. Click Submit. This returns you to the node-specific screen with the fence methods and fence instances displayed, showing that each device will power the system off in sequence and power the system on in sequence. This is shown in Figure 4.2, "Dual-Power Fencing Configuration".
    Dual-Power Fencing Configuration
    Dual-power fencing configuration

    Figure 4.2. Dual-Power Fencing Configuration


(Sebelumnya) 2 : Fence Configuration Guide2 : Chapter 5. Fence Devices - ... (Berikutnya)