Managing Serviceguard 14th Edition, June 2007

Building an HA Cluster Configuration
Managing the Running Cluster
Chapter 5268
Managing a Single-Node Cluster
The number of nodes you will need for your Serviceguard cluster depends
on the processing requirements of the applications you want to protect.
You may want to configure a single-node cluster to take advantage of
Serviceguard’s network failure protection.
In a single-node cluster, a cluster lock is not required, since there is no
other node in the cluster. The output from the cmquerycl command
omits the cluster lock information area if there is only one node.
You still need to have redundant networks, but you do not need to specify
any heartbeat LANs, since there is no other node to send heartbeats to.
In the cluster configuration ASCII file, specify all LANs that you want
Serviceguard to monitor. For LANs that already have IP addresses,
specify them with the STATIONARY_IP keyword, rather than the
HEARTBEAT_IP keyword. For standby LANs, all that is required is the
NETWORK_INTERFACE keyword with the LAN device name.
Single-Node Operation
Single-node operation occurs in a single-node cluster or in a multi-node
cluster, following a situation where all but one node has failed, or where
you have shut down all but one node, which will probably have
applications running. As long as the Serviceguard daemon cmcld is
active, other nodes can re-join the cluster at a later time.
If the Serviceguard daemon fails when in single-node operation, it will
leave the single node up and your applications running. This is different
from the loss of the Serviceguard daemon in a multi-node cluster, which
halts the node with a system reset, and causes packages to be switched
to adoptive nodes.
It is not necessary to halt the single node in this scenario, since the
application is still running, and no other node is currently available for
package switching.
However, you should not try to restart Serviceguard, since data
corruption might occur if the node were to attempt to start up a new
instance of the application that is still running on the node. Instead of
restarting the cluster, choose an appropriate time to shutdown and
reboot the node, which will allow the applications to shut down and then
permit Serviceguard to restart the cluster after rebooting.