Active Connection Counting

Nobody seems to have any other ideas, so i'll share my new solution... 😄

What it does is compares the number of current connections for a pool against a connection limit and, if it is exceeded, disables all pool members so that any new connections are redirected to a sorry page (configured in the profile). Existing and persistent connections are allowed to continue using the application. When the number of connections falls below the limit again, all pool members are switched back to active to allow new connections.

I've used a health monitor instead of an iRule, using 4 variables configured through the Management GUI:

virtualServerName - The name of the virtual server you want to monitor.
poolName          - The name of the pool you want to monitor.
poolMembers       - Names of pool members separated by a space.
memberLimit       - The number of connections each member (specified above)
                    can accept, separated by a space.

poolMembers

and

memberLimit

are converted to an array in the script.

The health monitor is an External monitor comprising of the following:

!/bin/sh
poolConnGrab=`bigpipe virtual ${virtualServerName} | grep conns | head -1`
currConns=`expr "$poolConnGrab" : '[^0-9]*\([0-9]*\)'`
connLimit=0
limitCount=0
memberLimit=(${memberLimit})
for poolMember in ${poolMembers}
do
  logger "Pool Member ${poolMember}"
  
  if bigpipe virtual ${virtualServerName} | grep ${poolMember} | grep -q "UP"
    then
      logger "Server Is Up. Increasing Connection Limit."
      connLimit=`expr $connLimit + ${memberLimit[${limitCount}]}`
    else
      logger "Server is Down!"
  fi
  limitCount=`expr $limitCount + 1`
done
logger "Utilisation: ${currConns} of ${connLimit}"
if [ $currConns -lt $connLimit ]
  then
    logger "Connections ACCEPTABLE"
    for poolMember in ${poolMembers}
    do
        bigpipe pool ${poolName} member ${poolMember} session enable
    done
else
    logger "Connections UNACCEPTABLE"
    for poolMember in ${poolMembers}
    do
        bigpipe pool ${poolName} member ${poolMember} session disable
    done
fi
echo "up"
exit 0

This works quite well for a global connection limit on a pool, and then using a ratio algorithm on the pool members. This script logs to /var/log/messages.

There's still room for improvement (like detecting if a member is already, for example, disabled and, if so, don't bother running the command again to disable it).