Checking the Reliability of the Service

The probe itself is an infinite while loop of nslookup commands. Before the while loop, a temporary file is set up to hold the nslookup replies. The probefail and retries variables are initialized to 0.

# Set up a temporary file for the nslookup replies.
DNSPROBEFILE=/tmp/.$RESOURCE_NAME.probe
probefail=0
retries=0

The while loop carries out the following tasks:

• Sets the sleep interval for the probe

• Uses hatimerun to start nslookup, passes the Probe_timeout value, and identifies the target host

• Sets the probefail variable based on the success or failure of the nslookup return code

• If probefail is set to 1 (failure), verifies that the reply to nslookup came from the sample data service and not some other DNS server

Here is the while loop code.

while :
do
   # The interval at which the probe needs to run is specified in the
   # property THOROUGH_PROBE_INTERVAL. Therefore, set the probe to sleep
   # for a duration of THOROUGH_PROBE_INTERVAL.
   sleep $PROBE_INTERVAL

   # Run an nslookup command of the IP address on which DNS is serving.
   hatimerun -t $PROBE_TIMEOUT /usr/sbin/nslookup $DNS_HOST $DNS_HOST \
   > $DNSPROBEFILE 2>&1

      retcode=$?
      if [ $retcode -ne 0 ]; then
            probefail=1
      fi

   # Make sure that the reply to nslookup comes from the HA-DNS
   # server and not from another nameserver mentioned in the 
   # /etc/resolv.conf file.
   if [ $probefail -eq 0 ]; then
# Get the name of the server that replied to the nslookup query.
   SERVER=` awk ' $1=="Server:" { print $2 }' \
   $DNSPROBEFILE | awk -F. ' { print $1 } ' `
   if [ -z "$SERVER" ]; then
      probefail=1
      else
         if [ $SERVER != $DNS_HOST ]; then
            probefail=1
         fi
   fi
fi