Managing HP Serviceguard for Linux, Tenth Edition, September 2012

networking parameters for the cluster heartbeat, cluster lock information, and timing
parameters (discussed in detail in Chapter 4 (page 91) ). Cluster parameters are entered
by editing the cluster configuration file (see “Configuring the Cluster” (page 179)). The
parameters you enter are used to build a binary configuration file which is propagated
to all nodes in the cluster. This binary cluster configuration file must be the same on all
the nodes in the cluster.
Heartbeat Messages
Central to the operation of the cluster manager is the sending and receiving of heartbeat
messages among the nodes in the cluster. Each node in the cluster exchanges UDP
heartbeat messages with every other node over each IP network configured as a heartbeat
device.
If a cluster node does not receive heartbeat messages from all other cluster nodes within
the prescribed time, a cluster re-formation is initiated; see “What Happens when a Node
Times Out” (page 87). At the end of the re-formation, if a new set of nodes form a cluster,
that information is passed to the package coordinator (described later in this chapter,
under “How the Package Manager Works” (page 44)). Failover packages that were
running on nodes that are no longer in the new cluster are transferred to their adoptive
nodes.
If heartbeat and data are sent over the same LAN subnet, data congestion may cause
Serviceguard to miss heartbeats and initiate a cluster re-formation that would not otherwise
have been needed. For this reason, HP recommends that you dedicate a LAN for the
heartbeat as well as configuring heartbeat over the data network.
Each node sends its heartbeat message at a rate calculated by Serviceguard on the basis
of the value of the MEMBER_TIMEOUT parameter, set in the cluster configuration file,
which you create as a part of cluster configuration.
IMPORTANT: When multiple heartbeats are configured, heartbeats are sent in parallel;
Serviceguard must receive at least one heartbeat to establish the health of a node. HP
recommends that you configure all subnets that interconnect cluster nodes as heartbeat
networks; this increases protection against multiple faults at no additional cost.
Heartbeat IP addresses must be on the same subnet on each node, but it is possible to
configure a cluster that spans subnets; see “Cross-Subnet Configurations” (page 27). See
HEARTBEAT_IP, under “Cluster Configuration Parameters ” (page 103), for more
information about heartbeat requirements. For timeout requirements and recommendations,
see the MEMBER_TIMEOUT parameter description in the same section. For troubleshooting
information, see “Cluster Re-formations Caused by MEMBER_TIMEOUT Being Set too
Low” (page 300). See also “Cluster Daemon: cmcld” (page 34).
38 Understanding Serviceguard Software Components