Use iRules to query number of active connections against a node

Okay, so give this a shot:

Shell script:

!/bin/bash

 user-defined: dns_server
dns_server="10.80.0.200"

 user-defined: host to resolve
host="tester.mydomain.com"

 user-defined: host port
host_port="80"

 user-defined: pool to update
pool="tester-pool"

lookup=($(dig @$dns_server $host +short))

 pre-define host_list
host_list=""

for x in ${lookup[@]}
do
    host_list="$host_list $x:$host_port"
done

if [ "$host_list" != "" ]
then
    tmsh modify ltm pool $pool members replace-all-with { $host_list }
fi

Create a cli script to point to the shell script:

> tmsh create sys icall script update-pool

create script update-pool {
    app-service none
    definition {
        set update [catch {exec /config/dev/archive/update-pool.sh}]
    }
    description none
    events none
}

** modify the above to point to your shell script

Create a periodic iCall:

create sys icall handler periodic update-pool script update-pool status active interval 300

This will create a periodic (I know I said "perpetual" but I meant periodic) script to completely update the given pool with the returned DNS values.