Managing HP Serviceguard for Linux, Eighth Edition, March 2008

Planning and Documenting an HA Cluster
Package Configuration Planning
Chapter 4 137
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.
Configuring a Package to Fail Over across Subnets: Example
To configure a package to fail over across subnets, you need to make
some additional edits to the package configuration file.
NOTE This section provides an example for a modular package; for legacy
packages, see “Configuring Cross-Subnet Failover” on page 286.
Suppose that you want to configure a package, pkg1, so that it can fail
over among all the nodes in a cluster comprising NodeA, NodeB, NodeC,
and NodeD.
NodeA and NodeB use subnet 15.244.65.0, which is not used by NodeC
and NodeD; and NodeC and NodeD use subnet 15.244.56.0, which is not
used by NodeA and NodeB. (See “Obtaining Cross-Subnet Information” on
page 175 for sample cmquerycl output).
Configuring node_name First you need to make sure that pkg1 will
fail over to a node on another subnet only if it has to. For example, if it is
running on NodeA and needs to fail over, you want it to try NodeB, on the
same subnet, before incurring the cross-subnet overhead of failing over
to NodeC or NodeD.