6.11. Fencing Topologies

⁠6.11. Fencing Topologies

Pacemaker supports fencing nodes with multiple devices through a feature called fencing topologies. Fencing topologies may be used to provide alternative devices in case one fails, or to require multiple devices to all be executed successfully in order to consider the node successfully fenced, or even a combination of the two.

Create the individual devices as you normally would, then define one or more fencing-level entries in the fencing-topology section of the configuration.

Each fencing level is attempted in order of ascending index. Allowed values are 1 through 9.
If a device fails, processing terminates for the current level. No further devices in that level are exercised, and the next level is attempted instead.
If the operation succeeds for all the listed devices in a level, the level is deemed to have passed.
The operation is finished when a level has passed (success), or all levels have been attempted (failed).
If the operation failed, the next step is determined by the scheduler and/or the controller.

Some possible uses of topologies include:

Try on-board IPMI, then an intelligent power switch if that fails
Try fabric fencing of both disk and network, then fall back to power fencing if either fails
Wait up to a certain time for a kernel dump to complete, then cut power to the node

⁠

Table 6.2. Properties of Fencing Levels

Field	Description
`id`	A unique name for the level
`target`	The name of a single node to which this level applies
`target-pattern`	An extended regular expression (as defined in POSIX) matching the names of nodes to which this level applies
`target-attribute`	The name of a node attribute that is set (to `target-value`) for nodes to which this level applies
`target-value`	The node attribute value (of `target-attribute`) that is set for nodes to which this level applies
`index`	The order in which to attempt the levels. Levels are attempted in ascending order until one succeeds. Valid values are 1 through 9.
`devices`	A comma-separated list of devices that must all be tried for this level

⁠

Example 6.3. Fencing topology with different devices for different nodes

 <cib crm_feature_set="3.0.6" validate-with="pacemaker-1.2" admin_epoch="1" epoch="0" num_updates="0">
  <configuration>
    ...
    <fencing-topology>
      <!-- For pcmk-1, try poison-pill and fail back to power -->
      <fencing-level id="f-p1.1" target="pcmk-1" index="1" devices="poison-pill"/>
      <fencing-level id="f-p1.2" target="pcmk-1" index="2" devices="power"/>

      <!-- For pcmk-2, try disk and network, and fail back to power -->
      <fencing-level id="f-p2.1" target="pcmk-2" index="1" devices="disk,network"/>
      <fencing-level id="f-p2.2" target="pcmk-2" index="2" devices="power"/>
    </fencing-topology>
    ...
  <configuration>
  <status/>
</cib>

⁠6.11.1. Example Dual-Layer, Dual-Device Fencing Topologies

The following example illustrates an advanced use of fencing-topology in a cluster with the following properties:

3 nodes (2 active prod-mysql nodes, 1 prod_mysql-rep in standby for quorum purposes)
the active nodes have an IPMI-controlled power board reached at 192.0.2.1 and 192.0.2.2
the active nodes also have two independent PSUs (Power Supply Units) connected to two independent PDUs (Power Distribution Units) reached at 198.51.100.1 (port 10 and port 11) and 203.0.113.1 (port 10 and port 11)
the first fencing method uses the fence_ipmi agent
the second fencing method uses the fence_apc_snmp agent targetting 2 fencing devices (one per PSU, either port 10 or 11)
fencing is only implemented for the active nodes and has location constraints
fencing topology is set to try IPMI fencing first then default to a "sure-kill" dual PDU fencing

In a normal failure scenario, STONITH will first select fence_ipmi to try to kill the faulty node. Using a fencing topology, if that first method fails, STONITH will then move on to selecting fence_apc_snmp twice:

once for the first PDU
again for the second PDU

The fence action is considered successful only if both PDUs report the required status. If any of them fails, STONITH loops back to the first fencing method, fence_ipmi, and so on until the node is fenced or fencing action is cancelled.

First fencing method: single IPMI device

Each cluster node has it own dedicated IPMI channel that can be called for fencing using the following primitives:

<primitive class="stonith" id="fence_prod-mysql1_ipmi" type="fence_ipmilan">
  <instance_attributes id="fence_prod-mysql1_ipmi-instance_attributes">
    <nvpair id="fence_prod-mysql1_ipmi-instance_attributes-ipaddr" name="ipaddr" value="192.0.2.1"/>
    <nvpair id="fence_prod-mysql1_ipmi-instance_attributes-action" name="action" value="off"/>
    <nvpair id="fence_prod-mysql1_ipmi-instance_attributes-login" name="login" value="fencing"/>
    <nvpair id="fence_prod-mysql1_ipmi-instance_attributes-passwd" name="passwd" value="finishme"/>
    <nvpair id="fence_prod-mysql1_ipmi-instance_attributes-verbose" name="verbose" value="true"/>
    <nvpair id="fence_prod-mysql1_ipmi-instance_attributes-pcmk_host_list" name="pcmk_host_list" value="prod-mysql1"/>
    <nvpair id="fence_prod-mysql1_ipmi-instance_attributes-lanplus" name="lanplus" value="true"/>
  </instance_attributes>
</primitive>
<primitive class="stonith" id="fence_prod-mysql2_ipmi" type="fence_ipmilan">
  <instance_attributes id="fence_prod-mysql2_ipmi-instance_attributes">
    <nvpair id="fence_prod-mysql2_ipmi-instance_attributes-ipaddr" name="ipaddr" value="192.0.2.2"/>
    <nvpair id="fence_prod-mysql2_ipmi-instance_attributes-action" name="action" value="off"/>
    <nvpair id="fence_prod-mysql2_ipmi-instance_attributes-login" name="login" value="fencing"/>
    <nvpair id="fence_prod-mysql2_ipmi-instance_attributes-passwd" name="passwd" value="finishme"/>
    <nvpair id="fence_prod-mysql2_ipmi-instance_attributes-verbose" name="verbose" value="true"/>
    <nvpair id="fence_prod-mysql2_ipmi-instance_attributes-pcmk_host_list" name="pcmk_host_list" value="prod-mysql2"/>
    <nvpair id="fence_prod-mysql2_ipmi-instance_attributes-lanplus" name="lanplus" value="true"/>
  </instance_attributes>
</primitive>

Second fencing method: dual PDU devices

Each cluster node also has two distinct power channels controlled by two distinct PDUs. That means a total of 4 fencing devices configured as follows:

Node 1, PDU 1, PSU 1 @ port 10
Node 1, PDU 2, PSU 2 @ port 10
Node 2, PDU 1, PSU 1 @ port 11
Node 2, PDU 2, PSU 2 @ port 11

The matching fencing agents are configured as follows:

<primitive class="stonith" id="fence_prod-mysql1_apc1" type="fence_apc_snmp">
  <instance_attributes id="fence_prod-mysql1_apc1-instance_attributes">
    <nvpair id="fence_prod-mysql1_apc1-instance_attributes-ipaddr" name="ipaddr" value="198.51.100.1"/>
    <nvpair id="fence_prod-mysql1_apc1-instance_attributes-action" name="action" value="off"/>
    <nvpair id="fence_prod-mysql1_apc1-instance_attributes-port" name="port" value="10"/>
    <nvpair id="fence_prod-mysql1_apc1-instance_attributes-login" name="login" value="fencing"/>
    <nvpair id="fence_prod-mysql1_apc1-instance_attributes-passwd" name="passwd" value="fencing"/>
    <nvpair id="fence_prod-mysql1_apc1-instance_attributes-pcmk_host_list" name="pcmk_host_list" value="prod-mysql1"/>
  </instance_attributes>
</primitive>
<primitive class="stonith" id="fence_prod-mysql1_apc2" type="fence_apc_snmp">
  <instance_attributes id="fence_prod-mysql1_apc2-instance_attributes">
    <nvpair id="fence_prod-mysql1_apc2-instance_attributes-ipaddr" name="ipaddr" value="203.0.113.1"/>
    <nvpair id="fence_prod-mysql1_apc2-instance_attributes-action" name="action" value="off"/>
    <nvpair id="fence_prod-mysql1_apc2-instance_attributes-port" name="port" value="10"/>
    <nvpair id="fence_prod-mysql1_apc2-instance_attributes-login" name="login" value="fencing"/>
    <nvpair id="fence_prod-mysql1_apc2-instance_attributes-passwd" name="passwd" value="fencing"/>
    <nvpair id="fence_prod-mysql1_apc2-instance_attributes-pcmk_host_list" name="pcmk_host_list" value="prod-mysql1"/>
  </instance_attributes>
</primitive>
<primitive class="stonith" id="fence_prod-mysql2_apc1" type="fence_apc_snmp">
  <instance_attributes id="fence_prod-mysql2_apc1-instance_attributes">
    <nvpair id="fence_prod-mysql2_apc1-instance_attributes-ipaddr" name="ipaddr" value="198.51.100.1"/>
    <nvpair id="fence_prod-mysql2_apc1-instance_attributes-action" name="action" value="off"/>
    <nvpair id="fence_prod-mysql2_apc1-instance_attributes-port" name="port" value="11"/>
    <nvpair id="fence_prod-mysql2_apc1-instance_attributes-login" name="login" value="fencing"/>
    <nvpair id="fence_prod-mysql2_apc1-instance_attributes-passwd" name="passwd" value="fencing"/>
    <nvpair id="fence_prod-mysql2_apc1-instance_attributes-pcmk_host_list" name="pcmk_host_list" value="prod-mysql2"/>
  </instance_attributes>
</primitive>
<primitive class="stonith" id="fence_prod-mysql2_apc2" type="fence_apc_snmp">
  <instance_attributes id="fence_prod-mysql2_apc2-instance_attributes">
    <nvpair id="fence_prod-mysql2_apc2-instance_attributes-ipaddr" name="ipaddr" value="203.0.113.1"/>
    <nvpair id="fence_prod-mysql2_apc2-instance_attributes-action" name="action" value="off"/>
    <nvpair id="fence_prod-mysql2_apc2-instance_attributes-port" name="port" value="11"/>
    <nvpair id="fence_prod-mysql2_apc2-instance_attributes-login" name="login" value="fencing"/>
    <nvpair id="fence_prod-mysql2_apc2-instance_attributes-passwd" name="passwd" value="fencing"/>
    <nvpair id="fence_prod-mysql2_apc2-instance_attributes-pcmk_host_list" name="pcmk_host_list" value="prod-mysql2"/>
  </instance_attributes>
</primitive>

Location Constraints

To prevent STONITH from trying to run a fencing agent on the same node it is supposed to fence, constraints are placed on all the fencing primitives:

<constraints>
  <rsc_location id="l_fence_prod-mysql1_ipmi" node="prod-mysql1" rsc="fence_prod-mysql1_ipmi" score="-INFINITY"/>
  <rsc_location id="l_fence_prod-mysql2_ipmi" node="prod-mysql2" rsc="fence_prod-mysql2_ipmi" score="-INFINITY"/>
  <rsc_location id="l_fence_prod-mysql1_apc2" node="prod-mysql1" rsc="fence_prod-mysql1_apc2" score="-INFINITY"/>
  <rsc_location id="l_fence_prod-mysql1_apc1" node="prod-mysql1" rsc="fence_prod-mysql1_apc1" score="-INFINITY"/>
  <rsc_location id="l_fence_prod-mysql2_apc1" node="prod-mysql2" rsc="fence_prod-mysql2_apc1" score="-INFINITY"/>
  <rsc_location id="l_fence_prod-mysql2_apc2" node="prod-mysql2" rsc="fence_prod-mysql2_apc2" score="-INFINITY"/>
</constraints>

Fencing topology

Now that all the fencing resources are defined, it’s time to create the right topology. We want to first fence using IPMI and if that does not work, fence both PDUs to effectively and surely kill the node.

<fencing-topology>
  <fencing-level devices="fence_prod-mysql1_ipmi" id="fencing-2" index="1" target="prod-mysql1"/>
  <fencing-level devices="fence_prod-mysql1_apc1,fence_prod-mysql1_apc2" id="fencing-3" index="2" target="prod-mysql1"/>
  <fencing-level devices="fence_prod-mysql2_ipmi" id="fencing-0" index="1" target="prod-mysql2"/>
  <fencing-level devices="fence_prod-mysql2_apc1,fence_prod-mysql2_apc2" id="fencing-1" index="2" target="prod-mysql2"/>
</fencing-topology>

Please note, in fencing-topology, the lowest index value determines the priority of the first fencing method.

Final configuration

Put together, the configuration looks like this:

<cib admin_epoch="0" crm_feature_set="3.0.7" epoch="292" have-quorum="1" num_updates="29" validate-with="pacemaker-1.2">
  <configuration>
    <crm_config>
      <cluster_property_set id="cib-bootstrap-options">
        <nvpair id="cib-bootstrap-options-stonith-enabled" name="stonith-enabled" value="true"/>
        <nvpair id="cib-bootstrap-options-stonith-action" name="stonith-action" value="off"/>
        <nvpair id="cib-bootstrap-options-expected-quorum-votes" name="expected-quorum-votes" value="3"/>
       ...
      </cluster_property_set>
    </crm_config>
    <nodes>
      <node id="prod-mysql1" uname="prod-mysql1">
      <node id="prod-mysql2" uname="prod-mysql2"/>
      <node id="prod-mysql-rep1" uname="prod-mysql-rep1"/>
        <instance_attributes id="prod-mysql-rep1">
          <nvpair id="prod-mysql-rep1-standby" name="standby" value="on"/>
        </instance_attributes>
      </node>
    </nodes>
    <resources>
      <primitive class="stonith" id="fence_prod-mysql1_ipmi" type="fence_ipmilan">
        <instance_attributes id="fence_prod-mysql1_ipmi-instance_attributes">
          <nvpair id="fence_prod-mysql1_ipmi-instance_attributes-ipaddr" name="ipaddr" value="192.0.2.1"/>
          <nvpair id="fence_prod-mysql1_ipmi-instance_attributes-action" name="action" value="off"/>
          <nvpair id="fence_prod-mysql1_ipmi-instance_attributes-login" name="login" value="fencing"/>
          <nvpair id="fence_prod-mysql1_ipmi-instance_attributes-passwd" name="passwd" value="finishme"/>
          <nvpair id="fence_prod-mysql1_ipmi-instance_attributes-verbose" name="verbose" value="true"/>
          <nvpair id="fence_prod-mysql1_ipmi-instance_attributes-pcmk_host_list" name="pcmk_host_list" value="prod-mysql1"/>
          <nvpair id="fence_prod-mysql1_ipmi-instance_attributes-lanplus" name="lanplus" value="true"/>
        </instance_attributes>
      </primitive>
      <primitive class="stonith" id="fence_prod-mysql2_ipmi" type="fence_ipmilan">
        <instance_attributes id="fence_prod-mysql2_ipmi-instance_attributes">
          <nvpair id="fence_prod-mysql2_ipmi-instance_attributes-ipaddr" name="ipaddr" value="192.0.2.2"/>
          <nvpair id="fence_prod-mysql2_ipmi-instance_attributes-action" name="action" value="off"/>
          <nvpair id="fence_prod-mysql2_ipmi-instance_attributes-login" name="login" value="fencing"/>
          <nvpair id="fence_prod-mysql2_ipmi-instance_attributes-passwd" name="passwd" value="finishme"/>
          <nvpair id="fence_prod-mysql2_ipmi-instance_attributes-verbose" name="verbose" value="true"/>
          <nvpair id="fence_prod-mysql2_ipmi-instance_attributes-pcmk_host_list" name="pcmk_host_list" value="prod-mysql2"/>
          <nvpair id="fence_prod-mysql2_ipmi-instance_attributes-lanplus" name="lanplus" value="true"/>
        </instance_attributes>
      </primitive>
      <primitive class="stonith" id="fence_prod-mysql1_apc1" type="fence_apc_snmp">
        <instance_attributes id="fence_prod-mysql1_apc1-instance_attributes">
          <nvpair id="fence_prod-mysql1_apc1-instance_attributes-ipaddr" name="ipaddr" value="198.51.100.1"/>
          <nvpair id="fence_prod-mysql1_apc1-instance_attributes-action" name="action" value="off"/>
          <nvpair id="fence_prod-mysql1_apc1-instance_attributes-port" name="port" value="10"/>
          <nvpair id="fence_prod-mysql1_apc1-instance_attributes-login" name="login" value="fencing"/>
          <nvpair id="fence_prod-mysql1_apc1-instance_attributes-passwd" name="passwd" value="fencing"/>
          <nvpair id="fence_prod-mysql1_apc1-instance_attributes-pcmk_host_list" name="pcmk_host_list" value="prod-mysql1"/>
        </instance_attributes>
      </primitive>
      <primitive class="stonith" id="fence_prod-mysql1_apc2" type="fence_apc_snmp">
        <instance_attributes id="fence_prod-mysql1_apc2-instance_attributes">
          <nvpair id="fence_prod-mysql1_apc2-instance_attributes-ipaddr" name="ipaddr" value="203.0.113.1"/>
          <nvpair id="fence_prod-mysql1_apc2-instance_attributes-action" name="action" value="off"/>
          <nvpair id="fence_prod-mysql1_apc2-instance_attributes-port" name="port" value="10"/>
          <nvpair id="fence_prod-mysql1_apc2-instance_attributes-login" name="login" value="fencing"/>
          <nvpair id="fence_prod-mysql1_apc2-instance_attributes-passwd" name="passwd" value="fencing"/>
          <nvpair id="fence_prod-mysql1_apc2-instance_attributes-pcmk_host_list" name="pcmk_host_list" value="prod-mysql1"/>
        </instance_attributes>
      </primitive>
      <primitive class="stonith" id="fence_prod-mysql2_apc1" type="fence_apc_snmp">
        <instance_attributes id="fence_prod-mysql2_apc1-instance_attributes">
          <nvpair id="fence_prod-mysql2_apc1-instance_attributes-ipaddr" name="ipaddr" value="198.51.100.1"/>
          <nvpair id="fence_prod-mysql2_apc1-instance_attributes-action" name="action" value="off"/>
          <nvpair id="fence_prod-mysql2_apc1-instance_attributes-port" name="port" value="11"/>
          <nvpair id="fence_prod-mysql2_apc1-instance_attributes-login" name="login" value="fencing"/>
          <nvpair id="fence_prod-mysql2_apc1-instance_attributes-passwd" name="passwd" value="fencing"/>
          <nvpair id="fence_prod-mysql2_apc1-instance_attributes-pcmk_host_list" name="pcmk_host_list" value="prod-mysql2"/>
        </instance_attributes>
      </primitive>
      <primitive class="stonith" id="fence_prod-mysql2_apc2" type="fence_apc_snmp">
        <instance_attributes id="fence_prod-mysql2_apc2-instance_attributes">
          <nvpair id="fence_prod-mysql2_apc2-instance_attributes-ipaddr" name="ipaddr" value="203.0.113.1"/>
          <nvpair id="fence_prod-mysql2_apc2-instance_attributes-action" name="action" value="off"/>
          <nvpair id="fence_prod-mysql2_apc2-instance_attributes-port" name="port" value="11"/>
          <nvpair id="fence_prod-mysql2_apc2-instance_attributes-login" name="login" value="fencing"/>
          <nvpair id="fence_prod-mysql2_apc2-instance_attributes-passwd" name="passwd" value="fencing"/>
          <nvpair id="fence_prod-mysql2_apc2-instance_attributes-pcmk_host_list" name="pcmk_host_list" value="prod-mysql2"/>
        </instance_attributes>
      </primitive>
   </resources>
    <constraints>
      <rsc_location id="l_fence_prod-mysql1_ipmi" node="prod-mysql1" rsc="fence_prod-mysql1_ipmi" score="-INFINITY"/>
      <rsc_location id="l_fence_prod-mysql2_ipmi" node="prod-mysql2" rsc="fence_prod-mysql2_ipmi" score="-INFINITY"/>
      <rsc_location id="l_fence_prod-mysql1_apc2" node="prod-mysql1" rsc="fence_prod-mysql1_apc2" score="-INFINITY"/>
      <rsc_location id="l_fence_prod-mysql1_apc1" node="prod-mysql1" rsc="fence_prod-mysql1_apc1" score="-INFINITY"/>
      <rsc_location id="l_fence_prod-mysql2_apc1" node="prod-mysql2" rsc="fence_prod-mysql2_apc1" score="-INFINITY"/>
      <rsc_location id="l_fence_prod-mysql2_apc2" node="prod-mysql2" rsc="fence_prod-mysql2_apc2" score="-INFINITY"/>
    </constraints>
    <fencing-topology>
      <fencing-level devices="fence_prod-mysql1_ipmi" id="fencing-2" index="1" target="prod-mysql1"/>
      <fencing-level devices="fence_prod-mysql1_apc1,fence_prod-mysql1_apc2" id="fencing-3" index="2" target="prod-mysql1"/>
      <fencing-level devices="fence_prod-mysql2_ipmi" id="fencing-0" index="1" target="prod-mysql2"/>
      <fencing-level devices="fence_prod-mysql2_apc1,fence_prod-mysql2_apc2" id="fencing-1" index="2" target="prod-mysql2"/>
    </fencing-topology>
   ...
  </configuration>
</cib>