Managing HP Serviceguard for Linux, Sixth Edition, August 2006

Understanding Serviceguard Software Components
How the Cluster Manager Works
Chapter 340
Automatic Cluster Startup
An automatic cluster startup occurs any time a node reboots and joins
the cluster. This can follow the reboot of an individual node, or it may be
when all nodes in a cluster have failed, as when there has been an
extended power failure and all SPUs went down.
Automatic cluster startup will take place if the flag AUTOSTART_CMCLD is
set to 1 in the $SGCONF/cmcluster.rc file. When any node reboots with
this parameter set to 1, it will rejoin an existing cluster, or if none exists
it will attempt to form a new cluster.
Dynamic Cluster Re-formation
A dynamic re-formation is a temporary change in cluster membership
that takes place as nodes join or leave a running cluster. Re-formation
differs from reconfiguration, which is a permanent modification of the
configuration files. Re-formation of the cluster occurs under the following
conditions (not a complete list):
• An SPU or network failure was detected on an active node.
• An inactive node wants to join the cluster. The cluster manager
daemon has been started on that node.
• A node has been added to or deleted from the cluster configuration.
• The system administrator halted a node.
• A node halts because of a package failure.
• A node halts because of a service failure.
• Heavy network traffic prohibited the heartbeat signal from being
received by the cluster.
• The heartbeat network failed, and another network is not configured
to carry heartbeat.
Typically, re-formation results in a cluster with a different composition.
The new cluster may contain fewer or more nodes than in the previous
incarnation of the cluster.