Understanding Serviceguard Package Dependencies, April 2009

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Figure 1: Automatic mode example

Initial startup example

Let’s assume all the packages in Figure 1 above are down. If they all have auto_run enabled, pkg1,

pkg2, pkg3 and pkg5 start on node1 and pkg4 starts on node2. Pkg2 is the highest priority package

and prefers to run on node1. It requires pkg5 to run on the same node. So pkg2 and pkg5 will run on

node1. Pkg1 requires pkg2 to be up on the same node and it requires pkg4 to be down on the same

node. Since pkg1 has higher priority than pkg4, and pkg2 is running on node1, pkg1 will run on

node1. Pkg3 will start on node1 where pkg5 is running. Pkg4 prefers to run on node1. But it requires

pkg1 to be down on the same node. Since it has lower priority than pkg1 and pkg1 is running on

node1, pkg4 cannot run on node1. Since pkg5 is running on node1, pkg4’s any_node dependency

is satisfied on node2. So it will run on node2.

Package and node failure examples

In Figure 1 above, say pkg1, pkg2, pkg3, and pkg5 are running on node1 and pkg4 is running on

node2. The following sections provide examples of how Serviceguard responds to package and

node failures.

What if pkg1 fails?

If pkg1 fails, it will go down and not fail over, because it requires pkg2 to be running on the same

node. Since pkg2 has higher priority than pkg1, pkg1 cannot drag pkg2 to another node.

What if pkg2 fails?

Pkg2 is the highest-priority package on the dependency graph. So if both pkg2 and the package that

it depends on (pkg5) can run on node2, Serviceguard will halt or move any package in order to run

pkg2 on node2. That means that pkg1, pkg2 and pkg5 will have to be halted and moved. Since

pkg3 and pkg4 depend on pkg5, they will have to be halted also. Serviceguard will halt pkg1 before

pkg2 and will halt pkg2, pkg3 and pkg4 before pkg5 (this assumes the default value for the

successor_halt_timeout parameter; see the cmmakepkg manpage for the description of this

parameter). Once pkg5 is halted, Serviceguard will start pkg5 on node2. Then it will start pkg2 and

pkg3. Pkg1 will start on node node2 after pkg2 is up. Since pkg1 requires pkg4 to be down on the

same node and it has higher priority than pkg4, pkg4 starts on node1.

Same node

UP dep

Same node

DOWN dep

Any node

UP dep

Same node

UP dep

Same node

UP dep

Package name = pkg1

Nodes = node 1, node 2

Priority = 30

Package name = pkg4

Nodes = node 1, node 2

Priority = no_priority

Package name = pkg2

Nodes = node 1, node 2

Priority = 10

Package name = pkg5

Nodes = node 1, node 2

Priority = no_priority

Package name = pkg3

Nodes = node 1, node 2

Priority = 20