Notification scripts are executable programs that Keepalived invokes when a server changes state. You can implements notification scripts to perform actions such as reconfiguring a network interface or starting, reloading or stopping a service.

To invoke a notification script, include one the following lines inside a vrrp_instance or vrrp_sync_group section:

The following executable script could be used to handle the general-purpose version of notify:

#!/bin/bash

ENDSTATE=$3
NAME=$2
TYPE=$1

case $ENDSTATE in
    "BACKUP") # Perform action for transition to BACKUP state
              exit 0
              ;;
    "FAULT")  # Perform action for transition to FAULT state
              exit 0
              ;;
    "MASTER") # Perform action for transition to MASTER state
              exit 0
              ;;
    *)        echo "Unknown state ${ENDSTATE} for VRRP ${TYPE} ${NAME}"
              exit 1
              ;;
esac

Tracking scripts are programs that Keepalived runs at regular intervals, according to a vrrp_script definition:

vrrp_script script_name {
  script       "program_path arg ..."
  interval i  # Run script every i seconds
  fall f      # If script returns non-zero f times in succession, enter FAULT state
  rise r      # If script returns zero r times in succession, exit FAULT state
  timeout t   # Wait up to t seconds for script before assuming non-zero exit code
  weight w    # Reduce priority by w on fall
}

program_path is the full pathname of an executable script or binary.

You can use tracking scripts with a vrrp_instance section by specifying a track_script clause, for example:

vrrp_instance instance_name {
  state MASTER
  interface eth0
  virtual_router_id 21
  priority 200
  advert_int 1
  virtual_ipaddress {
    10.0.0.10/24
  }
  track_script {
    script_name
    ...
  }
}

If a configured script returns a non-zero exit code f times in succession, Keepalived changes the state of the VRRP instance or group to FAULT, removes the virtual IP address 10.0.0.10 from eth0, reduces the priority value by w and stops sending multicast VRRP packets. If the script subsequently returns a zero exit code r times in succession, the VRRP instance or group exits the FAULT state and transitions to the MASTER or BACKUP state depending on its new priority.

If you want a server to enter the FAULT state if one or more interfaces goes down, you can also use a track_interface clause, for example:

  track_interface {
    eth0
    eth1
  }

A possible application of tracking scripts is to deal with a potential split-brain condition in the case that some of the Keepalived servers lose communication. For example, a script could track the existence of other Keepalived servers or use shared storage or a backup communication channel to implement a voting mechanism. However, configuring Keepalived to avoid a split brain condition is complex and it is difficult to avoid corner cases where a scripted solution might not work.

For an alternative solution, see Section 17.12, “Making HAProxy Highly Available Using Oracle Clusterware”.