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| Resources and resource dependencies | ||
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Resources are hardware or software entities that make up the application. Resources include disk groups and file systems, network interface cards (NIC), IP addresses, and applications.
Resource dependencies indicate resources that depend on each other because of application or operating system requirements. Resource dependencies are graphically depicted in a hierarchy, also called a tree, where the resources higher up (parent) depend on the resources lower down (child).
Sample resource dependency graph shows the hierarchy for a database application.
Sample resource dependency graph
Click the thumbnail above to view full-sized image.
Resource dependencies determine the order in which resources are brought online or taken offline. For example, a disk group must be imported before volumes in the disk group start, and volumes must start before file systems are mounted. Conversely, file systems must be unmounted before volumes stop, and volumes must stop before disk groups are deported.
A parent is brought online after each child is brought online, and so on up the tree, until finally the application is started. Conversely, to take a managed application offline, you stop resources beginning at the top of the hierarchy. In this example, the application is stopped first, followed by the database application. Next the IP address and file systems can be stopped concurrently. These resources do not have any resource dependency between them, and so on down the tree.
Child resources must be online before parent resources can be brought online. Parent resources must be taken offline before child resources can be taken offline. If resources do not have parent-child interdependencies, they can be brought online or taken offline concurrently.