Managing Serviceguard A.11.20, March 2013

IMPORTANT: If you have not already done so, read the discussion of Simple Dependencies
(page 143) before you go on.
The interaction of the legal values of dependency_location and dependency_condition
creates the following possibilities:
• Same-node dependency: a package can require that another package be UP on the same
node.
This is the case covered in the section on Simple Dependencies (page 143).
• Different-node dependency: a package can require that another package be UP on a different
node.
• Any-node dependency: a package can require that another package be UP on any node in
the cluster.
• Same-node exclusion: a package can require that another package be DOWN on the same
node. (But this does not prevent that package from being UP on another node.)
• All-nodes exclusion: a package can require that another package be DOWN on all nodes in
the cluster.
Rules for Exclusionary Dependencies
• All exclusions must be mutual.
That is, if pkg1 requires pkg2 to be DOWN, pkg2 must also require pkg1 to be DOWN.
By creating an exclusionary relationship between any two packages, you ensure that only
one of them can be running at any time — either on a given node (same-node exclusion) or
throughout the cluster (all-nodes exclusion). A package can have an exclusionary relationship
with any number of other packages, but each such relationship must be mutual.
NOTE: Unexpected behavior may result if you simultaneously halt two packages that have
an exclusionary dependency on each other.
• Priority (discussed in detail under “Dragging Rules for Simple Dependencies” (page 144)) must
be set for at least one of the packages in an exclusionary relationship.
The higher-priority package can force the lower-priority package to halt or (in the case of a
same-node exclusion) move to another eligible node, if any.
• dependency_location must be either same_node or all_nodes, and must be the same
for both packages.
• Both packages must be failover packages whose failover_policy (page 241) is
configured_node.
Rules for different_node and any_node Dependencies
These rules apply to packages whose dependency_condition is UP and whose
dependency_location is different_node or any_node. For same-node dependencies,
148 Planning and Documenting an HA Cluster