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VMware, Inc. 13
Chapter 1 Introduction
Two instances of vCenter Server Heartbeat regularly send “I’m alive” messages and message
acknowledgments to one another over a dedicated network connection referred to as the VMware Channel to
detect interruptions in responsiveness. If the passive server detects that this monitoring process (referred to as
the heartbeat) has failed, it initiates a failover as illustrated in Figure 1-1.
Figure 1-1. Failover
A failover occurs when the passive server detects that the active server is no longer responding. This can occur
when the active server hardware fails, loses its network connections, or otherwise becomes unavailable. Rather
than the active server gracefully closing, the passive server determines that the active server has failed and
requires no further operations. In a failover, the passive server immediately assumes the active server role. The
failover process is discussed in detail later in this guide.
Network Protection
vCenter Server Heartbeat proactively monitors the network by polling up to three predefined nodes to ensure
that the active server is visible on the network. vCenter Server Heartbeat polls by default the primary DNS
server, the default gateway, and the global catalog server at regular intervals. If all three nodes fail to respond,
for example in the case of a network card or local switch failure, vCenter Server Heartbeat can initiate a
switchover, allowing the Secondary server to assume the active role and service clients.
Application Protection
vCenter Server Heartbeat running on the active server locally monitors vCenter Server and its services
(through the use of plug-ins) to verify that vCenter Server is operational and not in an unresponsive or stopped
state. This level of monitoring is fundamental in ensuring that vCenter Server remains available to users.
If vCenter Server should fail, vCenter Server Heartbeat first tries to restart the application on the active server
(1) in Figure 1-2.
If the application does not successfully restart, vCenter Server Heartbeat initiates a switchover (2) in
Figure 1-2. Refer to “vCenter Server Heartbeat Switchover and Failover Processes” on page 16 for further
information about the switchover process.