Mastering Keepalived: Step‑by‑Step Server Load Balancing on Linux

1. Planning

1.1 Server environment

Load balancer master and WEB server 1 real IP: 10.10.195.53

Load balancer backup and 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

This section describes only the installation and configuration of keepalived; Java and Tomcat setup are 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 service

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 Configure keepalived.conf

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

Master configuration (NodeA):

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 (NodeB):

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 /opt/tomcat.pid script

#!/bin/bash
#description: check tomcat service and decide whether stop keepalived
#edited by zzh: 2015-10-14

CATALINA_HOME=/users/shr/apache-tomcat-7.0.64
JAVA_HOME=/users/shr/util/JavaDir/jdk
export CATALINA_HOME
export JAVA_HOME

ps ax --width=1000 | grep "org.apache.catalina.startup.Bootstrap start" | grep -v "grep" | awk '{printf $1 " "}' | wc | awk '{print $2}' > tomcat_process_count.txt
read line < tomcat_process_count.txt

start_tomcat=$CATALINA_HOME/bin/startup.sh

if [ ${line} -lt 1 ]; then
    echo -n "===Starting tomcat===:"
    ${start_tomcat}
    echo "===tomcat start ok.==="
    sleep 3
    # check the tomcat status.
    ps ax --width=1000 | grep "org.apache.catalina.startup.Bootstrapstart" | grep -v "grep" | awk '{printf $1 " "}' | wc | awk '{print $2}' > 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 inspection

3.1 Normal startup

Run tail -f /var/log/messages on the master (10.10.195.53) to see keepalived start logs, including VRRP instance transitions to MASTER and gratuitous ARP announcements.

Similar logs appear on the backup server (10.10.195.190) showing it entering BACKUP state.

3.2 Master‑backup failover

Stopping keepalived on the master ( service keepalived stop) triggers the backup to become MASTER, as shown by VRRP logs indicating state transition and VIP assignment.

Starting keepalived again on the original master causes it to reclaim MASTER role, with corresponding logs.

4. View virtual IP

Use ip addr show to verify that the virtual IP 10.10.195.212 is present on the active interface.

5. Common errors

5.1 Invalid IP number count

Log messages such as “receive an invalid ip number count associated with VRID!” can be resolved by changing virtual_router_id to a different value in /etc/keepalived/keepalived.conf.

5.2 Missing space before '{'

If the backup does not set VIPs after entering BACKUP state, ensure there is a space before the opening brace in the configuration file.

6. Adding a Tomcat service script

The following init script can be placed in /etc/init.d/tomcat to manage Tomcat as a service.

#!/bin/bash
#chkconfig: 2345 10 90
#description: Starts and Stops the tomcat daemon
#edited by ZZH: 2015-10-14

CATALINA_HOME=/users/shr/apache-tomcat-7.0.64
JAVA_HOME=/users/shr/util/JavaDir/jdk
export CATALINA_HOME
export JAVA_HOME

start_tomcat=$CATALINA_HOME/bin/startup.sh
stop_tomcat=$CATALINA_HOME/bin/shutdown.sh

start() {
    echo -n "===Starting tomcat===:"
    ${start_tomcat}
    echo "===tomcat start ok.==="
}

stop() {
    echo -n "===Shutting down tomcat===:"
    ${stop_tomcat}
    echo "===tomcat stop ok.==="
}

status() {
    ps ax --width=1000 | grep "org.apache.catalina.startup.Bootstrap start" | grep -v "grep" | awk '{printf $1 " "}' | wc | awk '{print $2}' > tomcat_process_count.txt
    read line < tomcat_process_count.txt
    if [ $line -gt 0 ]; then
        echo "tomcat is running"
    else
        echo "tomcat is stopped"
    fi
}

case "$1" in
    start) start ;;
    stop) stop ;;
    restart) stop; sleep 1; start ;;
    status) status ;;
    *) echo "Usage: $0 {start|stop|restart|status}"; exit 1 ;;
esac

exit 0

Make the script executable and add it to startup:

sudo chmod 755 tomcat sudo chkconfig --add tomcat

Then control Tomcat with service tomcat start|stop|restart|status.