How to Set Up Keepalived for High‑Availability Load Balancing on RHEL 5

1. Planning

1.1 Server environment

Load balancer master / WEB server 1 real IP: 10.10.195.53

Load balancer backup / WEB server 2 real IP: 10.10.195.190

Virtual IP for the load balancer: 10.10.195.212

1.2 Software environment

OS: Red Hat Enterprise Linux Server release 5.6 (Tikanga)

keepalived: keepalived‑1.2.19

Java: jdk‑1.7.0_79

Tomcat: apache‑tomcat‑7.0.64

2. Load‑balancer configuration

Only the keepalived installation and configuration are described here; Java and Tomcat setup is omitted.

2.1 Install keepalived

tar -zxvf keepalived-1.2.19.tar.gz cd keepalived-1.2.19 ./configure --prefix=/usr/local/keepalived --disable-fwmark make make install

2.2 Deploy keepalived binaries and init scripts

cp /usr/local/keepalived/sbin/keepalived /usr/sbin/ cp /usr/local/keepalived/etc/sysconfig/keepalived /etc/sysconfig/ cp /usr/local/keepalived/etc/rc.d/init.d/keepalived /etc/init.d/ mkdir /etc/keepalived cp /usr/local/keepalived/etc/keepalived/keepalived.conf /etc/keepalived/ chkconfig --add keepalived chkconfig keepalived on

Control commands:

service keepalived restart service keepalived start service keepalived stop service keepalived status

2.3 Edit keepalived.conf

mv /etc/keepalived/keepalived.conf /etc/keepalived/keepalived.conf.bak vi /etc/keepalived/keepalived.conf

The master and backup configurations are almost identical; only the highlighted sections differ.

Master configuration

global_defs { router_id NodeA } vrrp_script chk_http_port { script "/opt/tomcat.pid" interval 5 weight 2 } vrrp_instance VI_1 { state MASTER interface eth0 virtual_router_id 52 priority 150 advert_int 1 authentication { auth_type PASS auth_pass 1111 } track_script { chk_http_port } virtual_ipaddress { 10.10.195.212 } }

Backup configuration

global_defs { router_id NodeB } vrrp_script chk_http_port { script "/opt/tomcat.pid"; interval 5; weight 2 } vrrp_instance VI_1 { state BACKUP interface eth0 virtual_router_id 52 priority 100 advert_int 1 authentication { auth_type PASS; auth_pass 1111 } track_script { chk_http_port } virtual_ipaddress { 10.10.195.212 } }

2.4 Tomcat health‑check script ( /opt/tomcat.pid )

#!/bin/bash #description: check tomcat service and decide whether to stop keepalived CATALINA_HOME=/users/shr/apache-tomcat-7.0.64 JAVA_HOME=/users/shr/util/JavaDir/jdk export CATALINA_HOME JAVA_HOME ps ax --width=1000 | grep "org.apache.catalina.startup.Bootstrap start" | grep -v grep | awk '{printf $1 " "}' | wc -l > tomcat_process_count.txt read line < tomcat_process_count.txt if [ ${line} -lt 1 ]; then echo "===Starting tomcat===:" ${CATALINA_HOME}/bin/startup.sh echo "===tomcat start ok.===" sleep 3 # check tomcat status again ps ax --width=1000 | grep "org.apache.catalina.startup.Bootstrap start" | grep -v grep | awk '{printf $1 " "}' | wc -l > tomcat_process_count.txt read line2 < tomcat_process_count.txt if [ ${line2} -lt 1 ]; then sudo service keepalived stop fi fi rm tomcat_process_count.txt # shell end

3. Log verification

Use tail -f /var/log/messages on the master (10.10.195.53) to see keepalived start‑up messages and VRRP state transitions. Similar logs appear on the backup (10.10.195.190).

4. Failover testing

Stop keepalived on the master ( service keepalived stop) – the backup becomes MASTER. Restart keepalived on the former master ( service keepalived start) – it re‑acquires MASTER role.

5. View virtual IP

ip addr show

Look for the 10.10.195.212/32 address on eth0.

6. Common errors and fixes

6.1 VRID conflict

Log shows “receive an invalid ip number count associated with VRID”. Change virtual_router_id in keepalived.conf to a different number.

6.2 Missing space in configuration

If the backup stays in BACKUP state without assigning VIPs, ensure there is a space after the opening brace { in the configuration file.

7. Tomcat service script (optional)

A sample /etc/init.d/tomcat script is provided to start, stop, restart and query status of Tomcat. It checks for the existence of catalina.sh, defines start, stop, and status functions, and registers the script with chkconfig.