Installation guide

</service>

Example D.5. NFS Service Set Up for Resource Reuse and Inheritance

If the service were flat (that is, with no parent/child relationships), it would need to be configured

as follows:

• The service would need four nfsclient resources — one per file system (a total of two for file

systems), and one per target machine (a total of two for target machines).

• The service would need to specify export path and file system ID to each nfsclient, which

introduces chances for errors in the configuration.

In Example D.5, “NFS Service Set Up for Resource Reuse and Inheritance” however, the NFS

client resources nfsclient:bob and nfsclient:jim are defined once; likewise, the NFS export

resource nfsexport:exports is defined once. All the attributes needed by the resources are

inherited from parent resources. Because the inherited attributes are dynamic (and do not

conflict with one another), it is possible to reuse those resources — which is why they are

defined in the resources block. It may not be practical to configure some resources in multiple

places. For example, configuring a file system resource in multiple places can result in mounting

one file system on two nodes, therefore causing problems.

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 D.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 D.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_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.

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