Lvs Components - Red Hat ENTERPRISE LINUX 5 - VIRTUAL SERVER ADMINISTRATION Manual

LVS Components

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.
1.6.1. LVS Components
Section 1.6.1.1, "pulse"
shows a detailed list of each software component in an LVS router.
1.6.1.1. 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.
1.6.1.2. 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 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.
1.6.1.3. ipvsadm
This service updates the IPVS routing table in the kernel. The lvs daemon sets up and administers
LVS by calling ipvsadm to add, change, or delete entries in the IPVS routing table.
1.6.1.4. 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.
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