keepalived

Notes:

If several backup servers have the same priority, the backup server with the highest IP address value becomes the master server.

Prerequisites:

1sysctl net.ipv4.ip_forward=1                     ## Enable IP Forwarding.
2modprobe ip_vs; lsmod | grep ip_vs               ## ip_vs module is present/loaded.
3echo ip_vs >> /etc/modules-load.d/modules.conf   ## Ensure ip_vs module is loaded on boot.
4sysctl net.ipv4.ip_nonlocal_bind=1               ## If something else needs to bind to the VIP. (eg: HAProxy, Load Balancer, etc.)

Example config:

Show Sample Config

## UNICAST:
vrrp_script curlLocalHost {
  script       "/bin/curlLocalHost.sh"
  weight -10
  interval 2
  fall 2
  rise 2
}

vrrp_instance VRRP1 {
    state BACKUP
    interface eth0
    virtual_router_id 41
    priority 100

    unicast_src_ip 77.9.61.[46/47/48]
    unicast_peer {
      77.9.61.46
      77.9.61.47
      77.9.61.48
    }

    virtual_ipaddress {
        77.9.61.45
    }

  track_script {
    curlLocalHost
  }
  
}

Example Track Script (curlLocalHost.sh):

#!/bin/bash
"/bin/curl localhost"