Health monitor to mark pool member up when a ping FAILS (inverse ping health check)

Hello.

Take into account that any output in the script execution will produce an UP state in the monitor. So, the best way to fix your problems is something like this.

#!/bin/bash
 
# Remove IPv6/IPv4 compatibility prefix (LTM passes addresses in IPv6 format)
IP=`echo $1 | sed 's/::ffff://'`
 
ping -c5 -W2 $IP 2>&1 > /dev/null
 
if [ $? -eq 1 ]
then
   rm -f $pidfile
   echo "UP"
else
   rm -f $pidfile
fi

Some additional doc about external monitors:

REF - https://devcentral.f5.com/s/articles/ltm-external-monitors-the-basics

I recommend you to use always this template for external monitors

REF - https://devcentral.f5.com/s/articles/template-for-external-monitors

The complete script with your particular scenario would be like this ->

#!/bin/bash
 
# Save as /usr/bin/monitors/custom_monitor.bash
# Make executable using chmod 700 custom_monitor.bash
 
# Use a custom shell command to perform a health check of the pool member IP address and port
 
# Log debug to local0.debug (/var/log/ltm)?
# Check if a variable named DEBUG exists from the monitor definition
# This can be set using a monitor variable DEBUG=0 or 1
if [ -n "$DEBUG" ]
then
   if [ $DEBUG -eq 1 ]; then echo "EAV `basename $0`: \$DEBUG: $DEBUG" | logger -p local0.debug; fi
else
   # If the monitor config didn't specify debug, enable/disable it here
   DEBUG=0
   #echo "EAV `basename $0`: \$DEBUG: $DEBUG" | logger -p local0.debug
fi
 
# Remove IPv6/IPv4 compatibility prefix (LTM passes addresses in IPv6 format)
IP=`echo $1 | sed 's/::ffff://'`
 
# Save the port for use in the shell command
PORT=$2
 
# Check if there is a prior instance of the monitor running
pidfile="/var/run/`basename $0`.$IP.$PORT.pid"
if [ -f $pidfile ]
then
   kill -9 `cat $pidfile` > /dev/null 2>&1
   echo "EAV `basename $0`: exceeded monitor interval, needed to kill ${IP}:${PORT} with PID `cat $pidfile`" | logger -p local0.error
fi
 
# Add the current PID to the pidfile
echo "$$" > $pidfile
 
# Debug
if [ $DEBUG -eq 1 ]
then
   ####  Customize the log statement here if you want to log the command run or the output ####
   echo "EAV `basename $0`: Running for ${IP}:${PORT} using custom command" | logger -p local0.debug
fi
 
ping -c5 -W2 $IP 2>&1 > /dev/null
 
if [ $? -eq 1 ]
then
   rm -f $pidfile
   if [ $DEBUG -eq 1 ]; then echo "EAV `basename $0`: Succeeded for ${IP}:${PORT}" | logger -p local0.debug; fi
   echo "UP"
else
   rm -f $pidfile
   if [ $DEBUG -eq 1 ]; then echo "EAV `basename $0`: Failed for ${IP}:${PORT}" | logger -p local0.debug; fi
fi

KR,

Dario.

Thanks for the response.

Are you saying that I should create the above script in a separate file as /usr/bin/monitors/custom_monitor.bash instead of uploading it as a custom monitor in the file section? If so, how do I call it then, and is the argument that I specify in the external monitor the IP address to ping? I want to ping a totally external address to see if it responds-NOT ping the actual pool member itself.

The reason for this is that I only want the pool/VS to be active if the external IP stops responding to ping, because that IP is tied to a remote site, and this VS needs to become active for that site if the IP stops responding.

I'm still a bit confused-when I run my script manually, I get no script output unless the IP does not to ping-that to me means what you said-that the monitor should be marked as down as long as the IP responds as there is no output.

It sounds like you are trying to set up a service redundancy/failover solution. If that is the case, in the absence of details of your business requirement, it could be suggested that you would be better off setting up a health monitor for your remote service with a more reliable protocol than ICMP; e.g. an HTTP service, which is much easier and handy to set up.