Managing HP Serviceguard for Linux Ninth Edition, April 2009

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 (page 206) - to indicate which nodes a subnet is configured on
— monitored_subnet_access (page 204) - 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” (page 259).)
• 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; failing over across subnets can take longer than failing
over on the same subnet. List the nodes in order of preference instead of using the
wildcard.
• Deploying applications in this environment requires careful consideration; see
“Implications for Application Deployment” (page 142).
• 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 (page 197) 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.
Implications for Application Deployment
Because the relocatable IP address will change when a package fails over to a node on
another subnet, you need to make sure of the following:
• The hostname used by the package is correctly remapped to the new relocatable
IP address.
• The application that the package runs must be configured so that the clients can
reconnect to the package’s new relocatable IP address.
In the worst case (when the server where the application was running is down),
the client may continue to retry the old IP address until TCP’s tcp_timeout is reached
(typically about ten minutes), at which point it will detect the failure and reset the
connection.
For more information, see the white paper Technical Considerations for Creating a
Serviceguard Cluster that Spans Multiple IP Subnets, at http://docs.hp.com -> High
Availability.
142 Planning and Documenting an HA Cluster