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13.5. Advanced STONITH Configurations

Some people consider that having one fencing device is a single point of failure [19]; others prefer removing the node from the storage and network instead of turning it off.
Whatever the reason, Pacemaker supports fencing nodes with multiple devices through a feature called fencing topologies.
Simply create the individual devices as you normally would, then define one or more fencing-level entries in the fencing-topology section of the configuration.
Some possible uses of topologies include:

Table 13.2. 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
A regular expression matching the names of nodes to which this level applies (since 1.1.14)
target-attribute
The name of a node attribute that is set (to target-value) for nodes to which this level applies (since 1.1.14)
target-value
The node attribute value (of target-attribute) that is set for nodes to which this level applies (since 1.1.14)
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 13.3. 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>

13.5.1. 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>


[19] Not true, since a node or resource must fail before fencing even has a chance to