Installation guide

Chapter 7. Linux Virtual Server Overview 95

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

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

router is still properly functioning. On the active 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

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 router does not receive a response from the active router, it initiates failover

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

(MAC address) of the backup node, sends a command to the active router via both the

public and private network interfaces to shut down the lvs daemon on the active router,

and starts the lvs daemon on the backup node to accept requests for the conﬁgured virtual

servers.

7.6.1. Components of an LVS Cluster

Section 7.6.1.1 pulse shows a detailed list of each software component in an LVS router.

7.6.1.1. pulse

This is the controlling process which starts all other daemons related to LVS routers. At

boot time, the daemon is started by the /etc/rc.d/init.d/pulse script. It then reads

the conﬁguration ﬁle /etc/sysconfig/ha/lvs.cf. On the active router, pulse starts

the LVS daemon. On the backup router, pulse determines the health of the active router

by executing a simple heartbeat at a user-conﬁgurable interval. If the active router fails to

respond after a user-conﬁgurable interval, it initiates failover. During failover, pulse on

the backup router instructs the pulse daemon on the active router to shut down all LVS

services, starts the send_arp program to reassign the ﬂoating IP addresses to the backup

router’s MAC address, and starts the lvs daemon.

7.6.1.2. lvs

The lvs daemon runs on the active LVS router once called by pulse. It reads the conﬁgu-

ration ﬁle /etc/sysconfig/ha/lvs.cf, calls the ipvsadm utility to build and maintain

the IPVS routing table, and assigns a nanny process for each conﬁgured LVS service. If

nanny reports a real server is down, lvs instructs the ipvsadm utility to remove the real

server from the IPVS routing table.