C.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 Example C.6, “Service 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 Example C.7, “Service foo Failure Recovery with __independent_subtree Attribute”, the __independent_subtree attribute is used to accomplish the following actions:

If script:script_one fails, restart script:script_one, script:script_two, and script:script_three.
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.

Example C.6. Service foo Normal Failure Recovery

<service name="foo">
      <script name="script_one" ...>
          <script name="script_two" .../>
      </script>
      <script name="script_three" .../>
</service>

Example C.7. Service foo Failure Recovery with `__independent_subtree` Attribute

<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>