D.4. Failure Recovery And Independent Subtrees; D.5. Debugging And Testing Services And Resource Ordering - Red Hat ENTERPRISE LINUX 5 - ADMINISTRATION Manual

Appendix D. HA Resource Behavior
resource in multiple places can result in mounting one file system on two nodes, therefore causing
problems.

D.4. Failure Recovery and Independent Subtrees

In most enterprise environments, the normal course of action for failure recovery of a service is to
restart the entire service if any component in the service fails. For example, in
foo Normal Failure Recovery", if any of the scripts defined in this service fail, the normal course
of action is to restart (or relocate or disable, according to the service recovery policy) the service.
However, in some circumstances certain parts of a service may be considered non-critical; it may be
necessary to restart only part of the service in place before attempting normal recovery. To accomplish
that, you can use the __independent_subtree attribute. For example, in
foo Failure Recovery with __independent_subtree
attribute is used to accomplish the following actions:
• If script:script_one fails, restart script:script_two and script:script_one.
• If script:script_two fails, restart just script:script_two.
• If script:script_three fails, restart script:script_one, script:script_two, and script:script_three.
• If script:script_four fails, restart the whole service.
<service name="foo">
<script name="script_one" ...>
<script name="script_two" .../>
</script>
<script name="script_three" .../>
</service>
Example D.6. Service foo Normal Failure Recovery
<service name="foo">
<script name="script_one" __independent_subtree="1" ...>
<script name="script_two" __independent_subtree="1" .../>
<script name="script_three" .../>
</script>
<script name="script_four" .../>
</service>
Example D.7. Service foo Failure Recovery with __independent_subtree Attribute
D.5. Debugging and Testing Services and Resource
Ordering
You can debug and test services and resource ordering with the rg_test utility. rg_test is a
command-line utility that is run from a shell or a terminal (it is not available in Conga or system-
Table D.2, "rg_test Utility Summary"
config-cluster.)
rg_test utility.
102
Attribute", the __independent_subtree
summarizes the actions and syntax for the
Example D.6, "Service
Example D.7, "Service