external mointor

As it seems you've discovered, monitors have always taken ANY output by the script to stdout as an indication that the node is responding as expected.

Your issue is most likely due to a change in the format of the pool member IP address as passed to the script by the monitor deamon: In BIG-IP v4, a dotted quad IPv4 address was passed. LTM instead passes an IPv4-mapped IPv6 address in the format of ::ffff:10.10.10.1 (for IPv4 address 10.10.10.1)

So to account for that when monitoring IPv4 nodes, you'll notice the sample_monitor shell script strips off the IPv6 prefix leaving only the IPv4 dot notation address:

node_ip=`echo $1 | sed 's/::ffff://'`

However, your script looks for a match of a v4 dotted-quad address with no leading or trailing characters, which fails, thus the value of $node is an empty list:

$node =~ m/^(\d+\.\d+\.\d+\.\d+)$/;
$node = $1; 

Replace those 2 lines instead with the following and you should be good to go with no other changes to your original script:

$node =~ m/(\d+\.\d+\.\d+\.\d+)$/;

(Grabs the end of $node if it matches the dotted-quad address format.)

(Props to Colin for assisting with the perl translation.)

Post back if you still have trouble and we'll dig in further.

/deb