For more information regarding the security incident at F5, the actions we are taking to address it, and our ongoing efforts to protect our customers, click here.

Forum Discussion

drhaskins's avatar
drhaskins
Icon for Nimbostratus rankNimbostratus
Oct 30, 2020

Issue with External monitor returning value

I am attempting to write an external monitor to determine which of our three databases is the "master." We need to first ssh to the server and then run a command. This command should return either...
application delivery
bash
Expect
External
LTM
monitor
Simon_Blakely's avatar
Simon_Blakely
Icon for Employee rankEmployee
Nov 01, 2020

You need to understand the behaviour of External monitors and stdout

K7444: Requirements for external monitor output

-----

Custom external monitors must observe the following output requirements:

  • If a server meets the external monitor criteria, the external monitor must send data to stdout.
  • Note: Any data on stdout results in an Available status. The data does not have to be specific to the condition of the server.
  • Note: Any standard output stops the script from running. To ensure that the necessary operations occur, F5 recommends that you clean up any temporary files, perform logging, etc., before the system performs the standard output operation.
  • If a server fails to meet the external monitor criteria, the external monitor must not send any data to stdout.

-----

Looking at your script, you have 

status=$?
 
 echo "$status"

This will terminate the script here, and mark the monitor as "Available".

If you need to log something from the script for development purposes, use *logger* to log into /var/log/ltm