Managing HP Serviceguard for Linux, Tenth Edition, September 2012

Failover
Under normal conditions, a fully operating Serviceguard cluster simply monitors the health
of the cluster's components while the packages are running on individual nodes. Any
host system running in the Serviceguard cluster is called an active node. When you create
the package, you specify a primary node and one or more adoptive nodes.When a
node or its network communications fails, Serviceguard can transfer control of the package
to the next available adoptive node. This situation is shown in Figure 1-2.
Figure 2 Typical Cluster After Failover
After this transfer, the package typically remains on the adoptive node as long the
adoptive node continues running. If you wish, however, you can configure the package
to return to its primary node as soon as the primary node comes back online. Alternatively,
you may manually transfer control of the package back to the primary node at the
appropriate time.
Figure 1-2 does not show the power connections to the cluster, but these are important
as well. In order to remove all single points of failure from the cluster, you should provide
as many separate power circuits as needed to prevent a single point of failure of your
nodes, disks and disk mirrors. Each power circuit should be protected by an uninterruptible
power source. For more details, refer to the section on “Power Supply Planning” in
Chapter 4, “Planning and Documenting an HA Cluster.”
What is Serviceguard for Linux? 21