Red Hat ENTERPRISE LINUX AS 2.1 Installation Manual page 112

112 Chapter 6:Linux Virtual Server Overview
If the backup router does not receive a response from the active router, it will initiate 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.
6.6.1 Components of an LVS Cluster
Below is a list and a description for each software component of an LVS router.
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.
lvs
The lvs daemon runs on the active LVS router once called by pulse. It reads the configuration file
/etc/sysconfig/ha/lvs.cf, calls the ipvsadm service to build and maintain the IPVS rout-
ing table, and assigns a nanny process for each configured LVS service. If nanny reports a real
server is down, lvs instructs the ipvsadm service to remove the real server from the kernel's IPVS
routing table.
ipvsadm
This service updates the IPVS routing table in the kernel. The lvs daemon sets up and administers
an LVS cluster by calling ipvsadm to add, change, or delete entries in the IPVS routing table.
nanny
The nanny monitoring daemon runs on the active LVS router. Through this daemon, the active router
determines the health of each real server and, optionally, monitors its workload. A separate process
runs for each service defined on each real server.
/etc/sysconfig/ha/lvs.cf
This is the LVS cluster configuration file. Directly or indirectly, all daemons get their configuration
information from this file.