Managing Serviceguard Eighteenth Edition, September 2010

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 201), and in particular the subsection “Implications for Application Deployment”
(page 202).
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 3-5 and
Figure 3-6. Figure 3-5 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.
70 Understanding Serviceguard Software Components