Simple KeepaliveD set up

So keepalived has been around for quite a while now .... however it is still a mystery to many.
So this is a very simple example of how keepalived can work with MySQL. Hopefully, this can help those with questions.

We will have a Simple master to slave set up. Meaning.. we write to one unless we have failover to the second for some event.

1st - install keepalived

# yum search keepalived

keepalived.x86_64 : Load balancer and high availability service

  Name and summary matches only, use "search all" for everything.

# yum -y install keepalived

You should now have an config file 

# ls -ltr /etc/keepalived/keepalived.conf 

Keep the original as you always backup .. right....

# cp /etc/keepalived/keepalived.conf /etc/keepalived/keepalived.conf.orig

So you need to figure out an ipaddress you can use for your virtual ip.  I picked 192.168.0.123 for this example. 

Next, we will set up a script to be used for our new config file. 

A few things I did here..

I left a .cnf file for keepalived and a log all in the /etc/keepalived.

This makes it simple for the example so you can do this or use your own cnf files.

A script:

cat /etc/keepalived/keepalived_check.sh 

#!/bin/bash

# monitor mysql status

# if this node mysql is dead

# and its slave is alive , then stop its keepalived. The other node will bind the IP.

export MYSQL_HOME=/etc/keepalived/

export PATH=$MYSQL_HOME/bin:$PATH

mysql="/usr/bin/mysql"

mysqladmin="/usr/bin/mysqladmin"

delay_file="$MYSQL_HOME/slave_delay_second.log"

slave_host=$1

ALIVE=$($mysqladmin --defaults-file=$MYSQL_HOME/.my.localhost.cnf  ping | grep alive | wc -l );

REMOTEALIVE=$($mysqladmin --defaults-file=$MYSQL_HOME/.my.remotehost.cnf  ping | grep alive | wc -l );

if [[ $ALIVE -ne 1 ]]

then

#echo "MySQL is down"

        if [[ $REMOTEALIVE -eq 1 ]]

        then

#        echo "Shutdown keep alive "

            systemctl stop keepalived  

#       echo " keepalived stop "

        fi

#else

#echo "MySQL is up"

#date

fi

exit 0 #all done

New config file

cat /etc/keepalived/keepalived.conf

global_defs {

      notification_email {

        anothermysqldba@gmail.com 

      }

      notification_email_from anothermysqldba@gmail.com 

      smtp_server localhost

      smtp_connect_timeout 30

      }

vrrp_script check_mysql {

   script "/etc/keepalived/keepalived_check.sh "

   interval 2

   weight 2

}

vrrp_instance VI_1 {

      state MASTER

      interface enp0s8  # <--- WHAT INTERFACE NAME HOLDS YOUR REAL IP /sbin/ifconfig

        # found with ip link show

      virtual_router_id 51

      priority 101

      advert_int 1

      nopreempt  # only needed on higher priority node

      authentication {

        auth_type PASS

        auth_pass 1111

      }

      track_script {

        check_mysql

      }

      virtual_ipaddress {

        192.168.0.123 

      }

}

This is all great but does it work....

So we have 2 hosts

[root@centosa keepalived]# hostname

centosa

[root@centosb keepalived]# hostname

centosb

Start keepalived  

[root@centosa keepalived]# systemctl status keepalived

● keepalived.service - LVS and VRRP High Availability Monitor

   Loaded: loaded (/usr/lib/systemd/system/keepalived.service; disabled; vendor preset: disabled)

   Active: inactive (dead)

[root@centosa keepalived]# systemctl restart keepalived

[root@centosa keepalived]# systemctl status keepalived

● keepalived.service - LVS and VRRP High Availability Monitor

   Loaded: loaded (/usr/lib/systemd/system/keepalived.service; disabled; vendor preset: disabled)

   Active: active (running)

[root@centosa keepalived]# ssh 192.168.0.123 'hostname'

root@192.168.0.123's password: 

centosa

Prove the connections work already

[root@centosa keepalived]# mysql --defaults-file=.my.remotehost.cnf --host=192.168.0.101   -e "select @@hostname"

+------------+

| @@hostname |

+------------+

| centosb    |

+------------+

[root@centosa keepalived]# mysql --defaults-file=.my.remotehost.cnf --host=192.168.0.102   -e "select @@hostname"

+------------+

| @@hostname |

+------------+

| centosa    |

+------------+

Double check that it is running... 

[root@centosa keepalived]# systemctl status keepalived | grep active

   Active: active 

[root@centosb keepalived]# systemctl status keepalived | grep active

   Active: active 

Test current VIP .. stop mysql and watch same VIP change hosts ... 

[root@centosa keepalived]# mysql --defaults-file=.my.remotehost.cnf --host=192.168.0.123   -e "select @@hostname"

+------------+

| @@hostname |

+------------+

| centosa    |

+------------+

[root@centosa keepalived]# systemctl stop mysqld 

[root@centosa keepalived]# mysql --defaults-file=.my.remotehost.cnf --host=192.168.0.123   -e "select @@hostname"

+------------+

| @@hostname |

+------------+

| centosb    |

+------------+