Multiple external health monitors do not work except one. Any alternative?

The issue has been resolved and I am sharing the solution for the people who may need multiple external monitors using SSH connection within their script.

Configuration and Environment

- BIG-IP version: 12.1.3.3

- Use multiple External monitors

- Script(External script file) include SSH connection to backend pool member on tcp port 22

Issues identified and its solution

- Issue 1: Redirection logging data to a file for the troubleshooting purpose doesn't work well.

Solution: Use logger command to send logging data to /var/log/ltm (Credit to Jie. Thanks Jie)

echo "`date` ${node_ip}: Script started" | logger -p local0.debug

-Issue 2: From the second SSH connection used in any external health monitors, it doesn't use the Client SSH cipher configuration under /config/ssh/ssh_config.

Ciphers aes128-cbc,aes256-cbc,aes256-ctr,aes128-ctr,aes192-ctr

Instead it starts using only ciphers aes128-cbc,aes256-cbc where the pool members (backend servers) require aes128-ctr,aes192-ctr,aes256-ctr. Because of this, SSH connection fails and finally ssh command returns 255, which says SSH connection failure - Refer to wireshark capture above

-Solution: Specify specific SSH ciphers within ssh command

RET_STATUS=`ssh -c aes128-ctr,aes192-ctr,aes256-ctr ${un}@${node_ip} -t "bash -l -c 'exit'" 2>/dev/null`

Thank you.