Red Hat ENTERPRISE LINUX 5 - ADMINISTRATION Manual page 111

D.3. Inheritance, the <resources> Block, and Reusing
Resources
Some resources benefit by inheriting values from a parent resource; that is commonly the case in an
Example D.5, "NFS Service Set Up for Resource Reuse and Inheritance"
NFS service.
NFS service configuration, set up for resource reuse and inheritance.
<resources>
<nfsclient name="bob" target="bob.test.com" options="rw,no_root_squash"/>
<nfsclient name="jim" target="jim.test.com" options="rw,no_root_squash"/>
<nfsexport name="exports"/>
</resources>
<service name="foo">
<fs name="1" mountpoint="/mnt/foo" device="/dev/sdb1" fsid="12344">
<nfsexport ref="exports">
attributes are inherited from the mountpoint and fsid
attribute of the parent fs resource -->
<nfsclient ref="bob"/> <!-- nfsclient's path is inherited
from the mountpoint and the fsid is added to the options
string during export -->
<nfsclient ref="jim"/ >
</nfsexport>
</fs>
<fs name="2" mountpoint="/mnt/bar" device="/dev/sdb2" fsid="12345">
<nfsexport ref="exports">
<nfsclient ref="bob"/> <!-- Because all of the critical
data for this resource is either defined in the resources block
or inherited, we can reference it again! -->
<nfsclient ref="jim"/>
</nfsexport>
</fs>
<ip address="10.2.13.20"/>
</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.
Example D.5, "NFS Service Set Up for Resource Reuse and Inheritance"
In
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
Inheritance, the <resources> Block, and Reusing Resources
<!-- nfsexport's path and fsid
shows a typical
however, the NFS
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