Mastering Keepalived: Step-by-Step HA Setup, Scripts, and Troubleshooting

1. Planning

Define server IPs: master/load balancer 10.10.195.53, backup 10.10.195.190, virtual IP 10.10.195.212.

2. Software Environment

OS: Red Hat Enterprise Linux 5.6; keepalived 1.2.19; JDK 1.7.0_79; Tomcat 7.0.64.

3. Install and Configure keepalived

Installation commands:

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

Copy binaries and config files, enable 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
service keepalived restart

3.1 keepalived.conf for Master

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
    }
}

3.2 keepalived.conf for Backup

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
    }
}

4. /opt/tomcat.pid script

#!/bin/bash
# description: check tomcat service and decide whether stop keepalived
CATALINA_HOME=/users/shr/apache-tomcat-7.0.64
JAVA_HOME=/users/shr/util/JavaDir/jdk
export CATALINA_HOME JAVA_HOME
# check tomcat process count
ps ax | grep "org.apache.catalina.startup.Bootstrap start" | grep -v grep | 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 again, stop keepalived if tomcat not running
    ps ax | grep "org.apache.catalina.startup.Bootstrap start" | grep -v grep | wc -l > tomcat_process_count.txt
    read line2 < tomcat_process_count.txt
    if [ $line2 -lt 1 ]; then
        service keepalived stop
    fi
fi
rm tomcat_process_count.txt

5. Log Checking and Failover

Use tail -f /var/log/messages to view keepalived logs. The logs show VRRP state transitions, VIP assignment, and gratuitous ARP messages. Stopping the master service triggers a failover to the backup, which then assumes MASTER state.

6. Common Errors

Error: “receive an invalid ip number count associated with VRID”. Fix by changing virtual_router_id to a unique value.

Error: Backup does not set VIP after entering BACKUP state. Ensure there is a space before the opening brace in the configuration file.

7. Tomcat Init Script (Optional)

A sample SysV init script for managing Tomcat is provided, including start, stop, restart, and status functions.