iApp monitor pool | multiple FQDN

Are you using server name indication on your SharePoint servers? We have an external (EAV) monitor that can do SNI.

What you could do is set up multiple pools containing the same pool members, one for each FQDN, and an iRule on the virtual server to distribute requests to the correct pool based on HTTP::host value.

Using a unique SNI EAV monitor on each pool would down that pool if a particular site collection was not responding. Here's an example of that monitor:

!/bin/sh
 These arguments supplied automatically for all external monitors:
 $1 = IP (nnn.nnn.nnn.nnn notation)
 $2 = port (decimal, host byte order)

 This script expects the following Name/Value pairs:
 HOST = the host name of the SNI-enabled site
 URI  = the URI to request
 RECV = the expected response

 Remove IPv6/IPv4 compatibility prefix (LTM passes addresses in IPv6 format)
NODE=`echo ${1} | sed 's/::ffff://'`
if [[ $NODE =~ ^[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}$ ]]; then
     node is v4
    NODE=${NODE}
else
     node is v6
    NODE=[${NODE}]
fi
PORT=${2}
PIDFILE="/var/run/`basename ${0}`.sni_monitor_${HOST}_${PORT}_${NODE}_sni.pid"
 kill of the last instance of this monitor if hung and log current pid
if [ -f $PIDFILE ]
then
   echo "EAV exceeded runtime needed to kill ${HOST}:${PORT}:${NODE}" | logger -p local0.error
   kill -9 `cat $PIDFILE` > /dev/null 2>&1
fi
curl-apd -k -v --resolve $HOST:$PORT:$NODE https://$HOST$URI 2>&1 > /dev/null | grep -i "${RECV}" 
STATUS=$?
rm -f $PIDFILE
if [ $STATUS -eq 0 ]
then
    echo "UP"
fi
exit