Installation guide

Chapter 1. Red Hat Cluster Suite Overview 23

• To balance the load across the real servers.

• To check the integrity of the services on each real server.

The backup LVS router monitors the active LVS router and takes over from it in case the

active LVS router fails.

Figure 1-19 provides an overview of the LVS components and their interrelationship.

Figure 1-19. Components of a Running LVS Cluster

The pulse daemon runs on both the active and passive LVS routers. On the backup LVS

router, pulse sends a heartbeat to the public interface of the active router to make sure the

active LVS router is properly functioning. On the active LVS router, pulse starts the lvs

daemon and responds to heartbeat queries from the backup LVS router.

Once started, the lvs daemon calls the ipvsadm utility to conﬁgure and maintain the

IPVS (IP Virtual Server) routing table in the kernel and starts a nanny process for each

conﬁgured virtual server on each real server. Each nanny process checks the state of one

conﬁgured service on one real server, and tells the lvs daemon if the service on that real

server is malfunctioning. If a malfunction is detected, the lvs daemon instructs ipvsadm

to remove that real server from the IPVS routing table.

If the backup LVS router does not receive a response from the active LVS router, it initiates

failover by calling send_arp to reassign all virtual IP addresses to the NIC hardware

addresses (MAC address) of the backup LVS router, sends a command to the active LVS