ICMP Custom Source Address Monitor

Problem this snippet solves:

This external monitor shows how to select a custom self IP address from the /config/bigip_base.conf to source ICMP pings from. The scenario is described in the following post:

How to setup external monitor with extended ping? http://devcentral.f5.com/Default.aspx?tabid=53&aft=1171280

How to use this snippet:

1. Create a new file containing the code below on the LTM filesystem. Recommended location is /usr/bin/monitors. Permissions on the file must be 700 or better, giving root rwx access to the file. Customize the self IP prefix to search for in the bigip_base.conf by replacing 10.41.1. in the script below

2. Create a monitor profile of type "External" with the following values:

   • External Program: . . the name of the script file created in step 1
   • Arguments: . . . . . .DEBUG=0 or DEBUG=1 to log debug messages to /var/log/ltm

If you add a DEBUG variable in the monitor definition and set it to 1, the script will write out debug to /var/log/ltm.

Example monitor definition:

# b monitor custom_ping_monitor list
monitor custom_ping_monitor {
   defaults from external
   DEBUG "0"
   run "custom_ping.bash"
}

3.Adjust the interval and timeout as appropriate for your application

Code :

#!/bin/bash

# Save as /usr/bin/monitors/custom_ping.bash
# Make executable using chmod 700 custom_ping.bash

# Use a custom IP address to source a ping to the pool member IP address
# Get the self IP address starting with 10.41.1. from the bigip_base.conf

# 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`: true: \$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`: false: \$DEBUG: $DEBUG" | logger -p local0.debug
fi

# Remove IPv6/IPv4 compatibility prefix (LTM passes addresses in IPv6 format)
IP=`echo $1 | sed 's/::ffff://'`

# We don't use the port except for logging
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 log of the command before it is run
if [ $DEBUG -eq 1 ]
then
   echo "EAV `basename $0`: Running for ${IP}:${PORT} using source IP `awk 'BEGIN {RS="}\n";FS=RS} /^self 10\.41\.1\./ {print $1;} ' /config/bigip_base.conf |head -1|awk '{print $2}'`" | logger -p local0.debug
fi

# Send the ping request and look for rtt in response
# Redirect stderr and stdout to nothing to ensure we don't errantly mark the pool member up
ping -I `awk 'BEGIN {RS="}\n";FS=RS} /^self 10\.41\.1\./ {print $1;}' /config/bigip_base.conf |head -1|awk '{print $2}'` -c 1 -W 1 $IP | grep rtt 2>&1 > /dev/null

# Check if the command ran successfully
# Note that any standard output will result in the script execution being stopped
# So do any cleanup before echoing to STDOUT
if [ $? -eq 0 ]
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