13.5. Advanced Fencing Configurations
Some people consider that having one fencing device is a single point of failure
, 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 and then define one or more fencing levels in the fencing-topology section in the configuration.
Each level is attempted in ascending index
order
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 Policy Engine and/or crmd.
Some possible uses of topologies include:
try poison-pill and fail back to power
try disk and network, and fall back to power if either fails
initiate a kdump and then poweroff the node
Table 13.2. Properties of Fencing Levels
Field
|
Description
|
---|
id
|
|
target
|
The node to which this level applies
|
index
|
The order in which to attempt the levels. Levels are attempted in ascending index order until one succeeds .
|
devices
|
A comma-separated list of devices that must all be tried for this level
|
13.5.1. Example use of Fencing Topologies
<cib crm_feature_set="3.0.6" validate-with="pacemaker-1.2" admin_epoch="1" epoch="0" num_updates="0">
<configuration>
...
<fencing-topology>
<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"/>
<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>