Managing HP Serviceguard for Linux, Eighth Edition, March 2008

Planning and Documenting an HA Cluster
Package Configuration Planning
Chapter 4136
About Cross-Subnet Failover
It is possible to configure a cluster that spans subnets joined by a router,
with some nodes using one subnet and some another. This is known as a
cross-subnet configuration (see “Cross-Subnet Configurations” on
page 30). In this context, you can configure packages to fail over from a
node on one subnet to a node on another.
The implications for configuring a package for cross-subnet failover are
as follows:
• For modular packages, you must configure two new parameters in
the package configuration file to allow packages to fail over across
subnets:
— ip_subnet_node (see page 218) - to indicate which nodes a
subnet is configured on
— monitored_subnet_access (see page 217) - to indicate whether
a monitored subnet is configured on all nodes (FULL) or only some
(PARTIAL). (Leaving monitored_subnet_access unconfigured for a
monitored subnet is equivalent to FULL.)
(For legacy packages, see “Configuring Cross-Subnet Failover” on
page 286.)
• You should not use the wildcard (*) for node_name in the package
configuration file, as this could allow the package to fail over across
subnets when a node on the same subnet is eligible. Instead, list the
nodes in order of preference.
• Deploying applications in this environment requires careful
consideration; see “Implications for Application Deployment” on
page 137.
•If a monitored_subnet is configured for PARTIAL
monitored_subnet_access in a package’s configuration file, it must
be configured on at least one of the nodes on the node_name list for
that package.
Conversely, if all of the subnets that are being monitored for this
package are configured for PARTIAL access, each node on the
node_name list must have at least one of these subnets configured.
— As in other cluster configurations, a package will not start on a
node unless the subnets configured on that node, and specified in
the package configuration file as monitored subnets, are up.