Managing Serviceguard A.11.20, March 2013

control script that is installed with Serviceguard; see Chapter 6: “Configuring Packages and Their
Services ” (page 232), for instructions for creating modular packages.
Deciding When and Where to Run and Halt Failover Packages
The package configuration file assigns a name to the package and includes a list of the nodes on
which the package can run.
Failover packages list the nodes in order of priority (i.e., the first node in the list is the highest
priority node). In addition, failover packages’ files contain three parameters that determine failover
behavior. These are the auto_run parameter, the failover_policy parameter, and the
failback_policy parameter.
Failover Packages’ Switching Behavior
The auto_run parameter (known in earlier versions of Serviceguard as the
PKG_SWITCHING_ENABLED parameter) defines the default global switching attribute for a failover
package at cluster startup: that is, whether Serviceguard can automatically start the package when
the cluster is started, and whether Serviceguard should automatically restart the package on a new
node in response to a failure. Once the cluster is running, the package switching attribute of each
package can be temporarily set with the cmmodpkg command; at reboot, the configured value
will be restored.
The auto_run parameter is set in the package configuration file.
A package switch normally involves moving a failover package and its associated IP addresses
to a new system on the same subnet. In this case, the new system must have the same subnet
configured and working properly; otherwise the package will not be started.
NOTE: 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. In this context,
you can configure packages to fail over from a node on one subnet to a node on another, and
you will need to configure a relocatable IP address for each subnet the package is configured to
start on; see “About Cross-Subnet Failover” (page 160), and in particular the subsection “Implications
for Application Deployment” (page 161).
When a package fails over, TCP connections are lost. TCP applications must reconnect to regain
connectivity; this is not handled automatically. Note that if the package is dependent on multiple
subnets, normally all of them must be available on the target node before the package will be
started. (In a cross-subnet configuration, all the monitored subnets that are specified for this package,
and configured on the target node, must be up.)
If the package has a dependency on a resource or another package, the dependency must be met
on the target node before the package can start.
The switching of relocatable IP addresses on a single subnet is shown in Figure 14 and Figure 15.
Figure 14 shows a two node cluster in its original state with Package 1 running on Node 1 and
Package 2 running on Node 2. Users connect to the node with the IP address of the package they
wish to use. Each node has a stationary IP address associated with it, and each package has an
IP address associated with it.
52 Understanding Serviceguard Software Components