--- keepalived ---

Step 1 – Install Required Packages
Use the following command to install required packages to configure Keepalived on the server.
# yum install gcc kernel-headers kernel-devel

Step 2 – Install Keepalived
Keepalived is available in centos base repository. Install it using yum command line tool.
# yum install keepalived
Keepalived configuration File: /etc/keepalived/keepalived.conf

Server One

! Configuration File for keepalived

global_defs {
   notification_email {
     chouck@binghamton.edu
   }
   notification_email_from root@hanfs1.cc.binghamton.edu

   smtp_server 127.0.0.1
   smtp_connect_timeout 30
   router_id hanfs1.cc.binghamton.edu
}

vrrp_instance VI_1 {
    state MASTER
    interface ens160
    virtual_router_id 51
    priority 101
    advert_int 1
    smtp_alert
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    virtual_ipaddress {
        128.226.136.106
    }
}

Server Two

! Configuration File for keepalived

global_defs {
   notification_email {
     chouck@binghamton.edu
   }
   notification_email_from root@hanfs1.cc.binghamton.edu

   smtp_server 127.0.0.1
   smtp_connect_timeout 30
   router_id hanfs1.cc.binghamton.edu
}

vrrp_instance VI_1 {
    state BACKUP
    interface ens160
    virtual_router_id 51
    priority 100
    advert_int 1
    smtp_alert
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    virtual_ipaddress {
        128.226.136.106
    }
}

Step 5 – Start KeepAlived
Start KeepAlived service using the following command and also configure to autostart on system boot.
# service keepalived start
# chkconfig keepalived on

Step 6 – Check Virtual IPs
By default virtual IP will be assigned to master server, In case of master gets down, it will automatically assign to the slave server. Use the following command to show assigned virtual IP on the interface.
# ip addr show ens160

Step 7 - Servers must talk to each other
Enable IP forwarding:
# echo "net.ipv4.ip_forward = 1" >> /etc/sysctl.conf
# sysctl -p
net.ipv4.ip_forward = 1

Enable and start the keepalived service on each server:
# systemctl enable keepalived
# systemctl start keepalived
# systemctl status keepalived
 
Manual of sorts: https://buildmedia.readthedocs.org/media/pdf/keepalived/stable/keepalived.pdf