6.7.3. 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. To configure a backup fencing method for a node, you configure two methods for a node, configuring a fence instance for each method.

Note

The order in which the system will use the fencing methods you have configured follows their order in the cluster configuration file. The first method you configure with the ccs command is the primary fencing method, and the second method you configure is the backup fencing method. To change the order, you can remove the primary fencing method from the configuration file, then add that method back.
Note that at any time you can print a list of fence methods and instances currently configured for a node by executing the following command. If you do not specify a node, this command will list the fence methods and instances currently configured for all nodes.
ccs -h host --lsfenceinst [node]
Use the following procedure to configure a node with a primary fencing method that uses a fence device named my_apc, which uses the fence_apc fencing agent, and a backup fencing device that uses a fence device named sanswitch1, which uses the fence_sanbox2 fencing agent. Since the sanswitch1 device is a storage-based fencing agent, you will need to configure unfencing for that device as well.
  1. Add a primary fence method for the node, providing a name for the fence method.
    ccs -h host --addmethod method node
    For example, to configure a fence method named APC as the primary method for the node node-01.example.com in the configuration file on the cluster node node-01.example.com, execute the following command:
    ccs -h node01.example.com --addmethod APC node01.example.com
    
  2. Add a fence instance for the primary method. You must specify the fence device to use for the node, the node this instance applies to, the name of the method, and any options for this method that are specific to this node:
    ccs -h host --addfenceinst fencedevicename node method [options]
    
    For example, to configure a fence instance in the configuration file on the cluster node node-01.example.com that uses the APC switch power port 1 on the fence device named my_apc to fence cluster node node-01.example.com using the method named APC, execute the following command:
    ccs -h node01.example.com --addfenceinst my_apc node01.example.com APC port=1
    
  3. Add a backup fence method for the node, providing a name for the fence method.
    ccs -h host --addmethod method node
    For example, to configure a backup fence method named SAN for the node node-01.example.com in the configuration file on the cluster node node-01.example.com, execute the following command:
    ccs -h node01.example.com --addmethod SAN  node01.example.com
    
  4. Add a fence instance for the backup method. You must specify the fence device to use for the node, the node this instance applies to, the name of the method, and any options for this method that are specific to this node:
    ccs -h host --addfenceinst fencedevicename node method [options]
    
    For example, to configure a fence instance in the configuration file on the cluster node node-01.example.com that uses the SAN switch power port 11 on the fence device named sanswitch1 to fence cluster node node-01.example.com using the method named SAN, execute the following command:
    ccs -h node01.example.com --addfenceinst sanswitch1 node01.example.com SAN port=11
    
  5. Since the sanswitch1 device is a storage-based device, you must configure unfencing for this device.
    ccs -h node01.example.com --addunfence sanswitch1 node01.example.com port=11 action=on
    
You can continue to add fencing methods as needed.
This procedure configures a fence device and a backup fence device for one node in the cluster. You will need to configure fencing for the other nodes in the cluster as well.
Example 6.4, “cluster.conf After Adding Backup Fence Methods ” shows a cluster.conf configuration file after you have added a power-based primary fencing method and a storage-based backup fencing method to each node in the cluster.

Example 6.4. cluster.conf After Adding Backup Fence Methods


<cluster name="mycluster" config_version="3">
   <clusternodes>
     <clusternode name="node-01.example.com" nodeid="1">
         <fence>
            <method name="APC">
              <device name="my_apc" port="1"/>
             </method>
            <method name="SAN">
	      <device name="sanswitch1" port="11"/>
             </method>
         </fence>
         <unfence>
             <device name="sanswitch1" port="11" action="on"/> 
         </unfence
     </clusternode>
     <clusternode name="node-02.example.com" nodeid="2">
         <fence>
            <method name="APC">
              <device name="my_apc" port="2"/>
            </method>
            <method name="SAN">
	      <device name="sanswitch1" port="12"/>
             </method>
         </fence>
         <unfence>
             <device name="sanswitch1" port="12" action="on"/> 
         </unfence
     </clusternode>
     <clusternode name="node-03.example.com" nodeid="3">
         <fence>
            <method name="APC">
              <device name="my_apc" port="3"/>
            </method>
            <method name="SAN">
	      <device name="sanswitch1" port="13"/>
             </method>
         </fence>
         <unfence>
             <device name="sanswitch1" port="13" action="on"/> 
         </unfence
     </clusternode>
   </clusternodes>
   <fencedevices>
        <fencedevice agent="fence_apc" ipaddr="apc_ip_example" login="login_example" name="my_apc" passwd="password_example"/>
        <fencedevice agent="fence_sanbox2" ipaddr="san_ip_example" login="login_example" name="sanswitch1" passwd="password_example"/>
   </fencedevices>
   <rm>
   </rm>
</cluster>

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, as described in Section 6.15, “Propagating the Configuration File to the Cluster Nodes”.

Note

The order in which the system will use the fencing methods you have configured follows their order in the cluster configuration file. The first method you configure is the primary fencing method, and the second method you configure is the backup fencing method. To change the order, you can remove the primary fencing method from the configuration file, then add that method back.