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Chapter 2. Configuring Fencing with the ccs Command
As of the Red Hat Enterprise Linux 6.1 release and later, the Red Hat High Availability Add-On provides support for the
ccs cluster configuration command. The ccs command allows an administrator to create, modify and view the cluster.conf cluster configuration file. You can use the ccs command to configure a cluster configuration file on a local file system or on a remote node. Using the ccs command, an administrator can also start and stop the cluster services on one or all of the nodes in a configured cluster.
This chapter describes how to configure the Red Hat High Availability Add-On cluster configuration file using the
ccs command.
This chapter consists of the following sections:
Note
Make sure that your deployment of High Availability Add-On meets your needs and can be supported. Consult with an authorized Red Hat representative to verify your configuration prior to deployment. In addition, allow time for a configuration burn-in period to test failure modes.
Note
This chapter references commonly used
cluster.conf elements and attributes. For a comprehensive list and description of cluster.conf elements and attributes, see the cluster schema at /usr/share/cluster/cluster.rng, and the annotated schema at /usr/share/doc/cman-X.Y.ZZ/cluster_conf.html (for example /usr/share/doc/cman-3.0.12/cluster_conf.html).
2.1. Configuring Fence Devices
Configuring fence devices consists of creating, updating, and deleting fence devices for the cluster. You must create and name the fence devices in a cluster before you can configure fencing for the nodes in the cluster. For information on configuring fencing for the individual nodes in the cluster, see Section 2.3, “Configuring Fencing for Cluster Members”.
Before configuring your fence devices, you may want to modify some of the fence daemon properties for your system from the default values. The values you configure for the fence daemon are general values for the cluster. The general fencing properties for the cluster you may want to modify are summarized as follows:
- The
post_fail_delayattribute 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. Thepost_fail_delaydefault value is0. Its value may be varied to suit cluster and network performance. - The
post-join_delayattribute is the number of seconds the fence daemon (fenced) waits before fencing a node after the node joins the fence domain. Thepost_join_delaydefault value is6. A typical setting forpost_join_delayis between 20 and 30 seconds, but can vary according to cluster and network performance.
You reset the values of the
post_fail_delay and post_join_delay attributes with the --setfencedaemon option of the ccs command. Note, however, that executing the ccs --setfencedaemon command overwrites all existing fence daemon properties.
For example, to configure a value for the
post_fail_delay attribute, execute the following command. This command will overwrite the values of all other existing fence daemon properties that you can set with this command.
ccs -h host --setfencedaemon post_fail_delay=value
To configure a value for the
post_join_delay attribute, execute the following command. This command will overwrite the values of all other existing fence daemon properties that you can set with this command.
ccs -h host --setfencedaemon post_join_delay=value
To configure a value for both the
post_join_delay attribute and the post_fail_delay attribute, execute the following command:
ccs -h host --setfencedaemon post_fail_delay=value post_join_delay=value
Note
For more information about the
post_join_delay and post_fail_delay attributes as well as the additional fence daemon properties you can modify, see the fenced(8) man page and see the cluster schema at /usr/share/cluster/cluster.rng, and the annotated schema at /usr/share/doc/cman-X.Y.ZZ/cluster_conf.html.
To configure a fence device for a cluster, execute the following command:
ccs -h host --addfencedev devicename [fencedeviceoptions]
For example, to configure an APC fence device in the configuration file on the cluster node
node-01 named myfence with an IP address of apc_ip_example, a login of login_example, and a password of password_example, execute the following command:
ccs -h node-01 --addfencedev myfence agent=fence_apc ipaddr=apc_ip_example login=login_example passwd=password_example
The following example shows the
fencedevices section of the cluster.conf configuration file after you have added this APC fence device:
<fencedevices>
<fencedevice agent="fence_apc" ipaddr="apc_ip_example" login="login_example" name="myfence" passwd="password_example"/>
</fencedevices>
When configuring fence devices for a cluster, you may find it useful to see a listing of available devices for your cluster and the options available for each device. You may also find it useful to see a listing of fence devices currently configured for your cluster. For information on using the
ccs command to print a list of available fence devices and options or to print a list of fence devices currently configured for your cluster, see Section 2.2, “Listing Fence Devices and Fence Device Options”.
To remove a fence device from your cluster configuration, execute the following command:
ccs -h host --rmfencedev fence_device_name
For example, to remove a fence device that you have named
myfence from the cluster configuration file on cluster node node-01, execute the following command:
ccs -h node-01 --rmfencedev myfence
If you need to modify the attributes of a fence device you have already configured, you must first remove that fence device then add it again with the modified attributes.
Note that when you have finished configuring all of the components of your cluster, you will need to sync the cluster configuration file to all of the nodes.
