Understanding Serviceguard Package Dependencies, April 2009

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Introduction ...................................................................................................................................2

Scope...........................................................................................................................................2

Package priority.............................................................................................................................2

Configuration.................................................................................................................................3

Configuration examples ...............................................................................................................4

Same node dependency example:..............................................................................................4

Different node dependency example...........................................................................................4

Any node dependency example.................................................................................................4

Same node exclusionary (down) dependency example:..................................................................4

All nodes exclusionary (down) dependency example .....................................................................5

Multiple dependency example ...................................................................................................5

Dependency behavior .....................................................................................................................6

Using the cmrunpkg command ......................................................................................................6

Using the cmhaltpkg command......................................................................................................7

Using the cmapplyconf command ..................................................................................................7

Using other commands.................................................................................................................7

Automatic mode..........................................................................................................................8

Automatic mode examples........................................................................................................8

Assigning priorities....................................................................................................................10

For more information.....................................................................................................................13

Understanding Serviceguard

Package Dependencies

April 2009

Summary of content (13 pages)

PAGE 1
Understanding Serviceguard Package Dependencies April 2009 Introduction ................................................................................................................................... 2 Scope........................................................................................................................................... 2 Package priority .............................................................................................................................
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Introduction Dependencies define runtime relationships between packages. Serviceguard evaluates dependencies while making package placement decisions. The dependency parameters in the package configuration file specify under what conditions the dependency is satisfied. For example, you can define a dependency for package A requiring that package B is running before package A is started on the same node, or requiring that package B must be down on all nodes before package A is run.
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Configuration The package parameters dependency_name, dependency_condition, and dependency_location define package dependencies. You configure these parameters in the configuration file of the dependent package. If you want pkg1 to depend on pkg2, you specify the dependency in the configuration file for pkg1. • dependency_name specifies the name of the dependency. This must be unique among dependency names specified by the package. For example, a dependency on pkg2 can be called “pkg2dep”.
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Configuration examples Same node dependency example: Pkg1 requires pkg2 to be up on the same node before it can start and in order to continue running. Include the following in the configuration file for pkg1: Dependency_name pkg2dep Dependency_condtion pkg2=up Dependency_location same_node Different node dependency example Pkg1 requires pkg2 to be up on a different node before it can start and in order to continue running.
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All nodes exclusionary (down) dependency example Pkg1 requires pkg2 to be down in the cluster before it can start and in order to continue running. This dependency is mutual. Pkg1 needs to define an all nodes “down” dependency on pkg2 and pkg2 needs to define an all nodes “down” dependency on pkg1. Both configuration files must be applied at the same time. Note that at least one of these packages must be assigned a numerical priority; the priority of both packages cannot be “no_priority”.
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Dependency behavior This section describes the rules Serviceguard uses in managing packages with dependencies. Using the cmrunpkg command The following rules apply when you run packages that have dependencies using the cmrunpkg command: • cmrunpkg will fail if running the packages specified on the command line will cause another package to halt. This means if you attempt to run a higher priority package using cmrunpkg, and this will lead to a lower priority package going down, the command will fail.
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Using the cmhaltpkg command The following rules apply when halting packages with dependencies using the cmhaltpkg command: • You can halt a package using cmhaltpkg command only if its non-exclusionary dependent packages are either down or specified on the cmhaltpkg command line. Non- exclusionary dependents are packages that have defined an "up" dependency on this package. The order in which you specify these packages on the command line does not matter.
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Automatic mode Serviceguard uses the following rules in managing packages with dependencies in automatic mode (that is, when Serviceguard itself is managing packages, rather than responding to commands that run and halt packages). 1. If pkg1 has a same-node, any-node, or different-node dependency on pkg2, and pkg2 fails over to another node, pkg1 will restart. If the dependency is same-node, pkg1 will follow pkg2 to the new node.
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Figure 1: Automatic mode example Package name = pkg3 Nodes = node 1, node 2 Priority = 20 Package name = pkg1 Nodes = node 1, node 2 Priority = 30 Same node UP dep Same node DOWN dep Package name = pkg2 Nodes = node 1, node 2 Priority = 10 Package name = pkg4 Nodes = node 1, node 2 Priority = no_priority Same node UP dep Same node UP dep Package name = pkg5 Nodes = node 1, node 2 Priority = no_priority Any node UP dep Initial startup example Let’s assume all the packages in Figure 1 above are dow
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What if pkg3 fails? If pkg3 fails on node1, it will halt and will not be failed over. In order for pkg3 to fail over to node2, it requires pkg5 on the same node. So it needs to drag pkg5 to node2. Pkg3 has higher priority than pkg5 and it can drag pkg5. Moving pkg5 to node2 means pkg2 will need to move to node2. So, pkg3 will have to drag pkg2 also. Pkg3 cannot drag pkg2 because pkg2 has higher priority. This shows that the rule for dragging applies to the entire dependency graph.
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• Assign the highest priority to pkgB. If pkgB is the highest priority, the priorities assigned to pkgA and pkgC do not matter. • Set pkgB's priority to 10, pkgA's to 20 and pkgC's to 30. 4. You have three packages. PkgA requires that pkgB run on the same node and pkgB requires that pkgC run on the same node. If pkgA fails, it should not affect pkgB. If pkgB fails, it should not affect pkgC. Neither pkgA nor pkgB should drag pkgC.
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5. You have 3 packages. Both pkgA and pkgB require pkgC to be UP on the same node. If pkgB fails, it should not affect pkgA. If pkgA fails, it should be able to drag pkgC to a node where both can run. If pkgA is not up, pkgB should be able to drag pkgC. • Assign the highest priority to pkgA. • Assign the 2nd highest priority to pkgB. • Set pkgA’s priority to 10, pkgB’s to 20 and pkgC’s to 30. 6. You have three packages. PkgA depends on pkgC on the same node. PkgB depends on pkgC on any node.
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For more information To learn more about HP Serviceguard Solutions for high availability and disaster recovery, please visit: www.hp.com/go/serviceguardsolutions For technical documentation: www.docs.hp.com/hpux/ha © Copyright 2005-2009 Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice. The only warranties for HP products and services are set forth in the express warranty statements accompanying such products and services.