PROBE Program Code Listing

The PROBE program checks the availability of the data service by using nslookup commands (see the nslookup(1M) man page). The Monitor_start callback method starts this program, and the Monitor_stop callback method stops it.

Example A-5 dns_probe Program

#!/bin/ksh
#pragma ident   “@(#)dns_probe   1.1   00/04/19”
#
# Probe method for HA-DNS.
#
# This program checks the availability of the data service using nslookup, which 
# queries the DNS server to look for the DNS server itself. If the server
# does not respond or if the query is replied to by some other server, 
# then the probe concludes that there is some problem with the data service
# and fails the service over to another node in the cluster. Probing is done
# at a specific interval set by THOROUGH_PROBE_INTERVAL in the RTR file. 

#pragma ident   “@(#)dns_probe   1.1   00/05/24”

###############################################################################
# Parse program arguments.
function parse_args # [args ...]
{
        typeset opt

        while getopts `R:G:T:' opt
        do
                case “$opt” in
                R)
                        # Name of the DNS resource.
                        RESOURCE_NAME=$OPTARG
                        ;;
                G)
                        # Name of the resource group in which the resource is
                        # configured.
                        RESOURCEGROUP_NAME=$OPTARG
                        ;;
                T)
                        # Name of the resource type.
                        RESOURCETYPE_NAME=$OPTARG
                        ;;
                *)
                    logger -p ${SYSLOG_FACILITY}.err \
                    -t [$RESOURCETYPE_NAME,$RESOURCEGROUP_NAME,$RESOURCE_NAME] \
                    “ERROR: Option $OPTARG unknown”
                     exit 1
                     ;;
                esac
        done
}

###############################################################################
# restart_service ()
#
# This function tries to restart the data service by calling the Stop method
# followed by the Start method of the dataservice. If the dataservice has
# already died and no tag is registered for the dataservice under PMF,
# then this function fails the service over to another node in the cluster.
#
function restart_service
{
        # To restart the dataservice, first, verify that the 
        # dataservice itself is still registered under PMF.
        pmfadm -q $PMF_TAG
        if [[ $? -eq 0 ]]; then
                # Since the TAG for the dataservice is still registered under
                # PMF, first stop the dataservice and start it back up again.
                # Obtain the Stop method name and the STOP_TIMEOUT value for
                # this resource.
                STOP_TIMEOUT=`scha_resource_get -O STOP_TIMEOUT \
                        -R $RESOURCE_NAME -G $RESOURCEGROUP_NAMÈ
                STOP_METHOD=`scha_resource_get -O STOP \
                        -R $RESOURCE_NAME -G $RESOURCEGROUP_NAMÈ
                hatimerun -t $STOP_TIMEOUT $RT_BASEDIR/$STOP_METHOD \
                        -R $RESOURCE_NAME -G $RESOURCEGROUP_NAME \
                        -T $RESOURCETYPE_NAME

                if [[ $? -ne 0 ]]; then
                        logger-p ${SYSLOG_FACILITY}.err -t [$SYSLOG_TAG] \
                                “${ARGV0} Stop method failed.”
                        return 1
                fi

                # Obtain the Start method name and the START_TIMEOUT value for
                # this resource.
                START_TIMEOUT=`scha_resource_get -O START_TIMEOUT \
                        -R $RESOURCE_NAME -G $RESOURCEGROUP_NAMÈ
                START_METHOD=`scha_resource_get -O START \
                        -R $RESOURCE_NAME -G $RESOURCEGROUP_NAMÈ
                hatimerun -t $START_TIMEOUT $RT_BASEDIR/$START_METHOD \
                        -R $RESOURCE_NAME -G $RESOURCEGROUP_NAME \
                        -T $RESOURCETYPE_NAME

                if [[ $? -ne 0 ]]; then
                        logger-p ${SYSLOG_FACILITY}.err -t [$SYSLOG_TAG] \
                                “${ARGV0} Start method failed.”
                        return 1
                fi

        else
                # The absence of the TAG for the dataservice 
                # implies that the dataservice has already
                # exceeded the maximum retries allowed under PMF. 
                # Therefore, do not attempt to restart the
                # dataservice again, but try to failover
                # to another node in the cluster.
                scha_control -O GIVEOVER -G $RESOURCEGROUP_NAME \
                        -R $RESOURCE_NAME
        fi

        return 0
}

###############################################################################
# decide_restart_or_failover ()
#
# This function decides the action to be taken upon the failure of a probe: 
# restart the data service locally or fail over to another node in the cluster.
#
function decide_restart_or_failover
{
   
   # Check if this is the first restart attempt.
   if [ $retries -eq 0 ]; then
         # This is the first failure. Note the time of 
         # this first attempt. 
         start_time=`$RT_BASEDIR/gettimè
         retries=`expr $retries + 1`
         # Because this is the first failure, attempt to restart
         # the data service.
         restart_service
         if [ $? -ne 0 ]; then
            logger -p ${SYSLOG_FACILITY}.err -t [$SYSLOG_TAG] \
                “${ARGV0} Failed to restart data service.”
            exit 1
         fi
   else
      # This is not the first failure
      current_time=`$RT_BASEDIR/gettimè
      time_diff=`expr $current_time - $start_timè
      if [ $time_diff -ge $RETRY_INTERVAL ]; then
         # This failure happened after the time window
         # elapsed, so reset the retries counter,
         # slide the window, and do a retry.
         retries=1
         start_time=$current_time
         # Because the previous failure occurred more than 
         # Retry_interval ago, attempt to restart the data service.
         restart_service
         if [ $? -ne 0 ]; then
            logger -p ${SYSLOG_FACILITY}.err -t [$SYSLOG_TAG \
                “${ARGV0} Failed to restart HA-DNS.”
            exit 1
         fi
      elif [ $retries -ge $RETRY_COUNT ]; then
         # Still within the time window,
         # and the retry counter expired, so fail over.
         retries=0
         scha_control -O GIVEOVER -G $RESOURCEGROUP_NAME \
             -R $RESOURCE_NAME
         if [ $? -ne 0 ]; then
            logger -p ${SYSLOG_FACILITY}.err -t [$SYSLOG_TAG] \
                “${ARGV0} Failover attempt failed.”
            exit 1
         fi
      else
         # Still within the time window,
         # and the retry counter has not expired,
         # so do another retry.
         retries=`expr $retries + 1`
         restart_service
         if [ $? -ne 0 ]; then
            logger -p ${SYSLOG_FACILITY}.err -t [$SYSLOG_TAG] \
                “${ARGV0} Failed to restart HA-DNS.”
            exit 1
         fi
      fi
fi
}

###############################################################################
# MAIN
###############################################################################

export PATH=/bin:/usr/bin:/usr/cluster/bin:/usr/sbin:/usr/proc/bin:$PATH

# Obtain the syslog facility to use to log messages.
SYSLOG_FACILITY=`scha_cluster_get -O SYSLOG_FACILITY`

# Parse the arguments that have been passed to this method
parse_args “$@”

PMF_TAG=$RESOURCE_NAME.named
SYSLOG_TAG=$RESOURCETYPE_NAME,$RESOURCEGROUP_NAME,$RESOURCE_NAME

# The interval at which probing is to be done is set in the system defined
# property THOROUGH_PROBE_INTERVAL. Obtain the value of this property with
# scha_resource_get
PROBE_INTERVAL=scha_resource_get -O THOROUGH_PROBE_INTERVAL \
-R $RESOURCE_NAME -G $RESOURCEGROUP_NAMÈ

# Obtain the timeout value allowed for the probe, which is set in the 
# PROBE_TIMEOUT extension property in the RTR file. The default timeout for
# nslookup is 1.5 minutes.
probe_timeout_info=`scha_resource_get -O Extension -R $RESOURCE_NAME \
-G $RESOURCEGROUP_NAME Probe_timeout`
PROBE_TIMEOUT=`echo $probe_timeout_info | awk `{print $2}'`

# Identify the server on which DNS is serving by obtaining the value
# of the NETWORK_RESOURCES_USED property of the resource.
DNS_HOST=`scha_resource_get -O NETWORK_RESOURCES_USED -R $RESOURCE_NAME \
-G $RESOURCEGROUP_NAMÈ

# Get the retry count value from the system defined property Retry_count
RETRY_COUNT =`scha_resource_get -O RETRY_COUNT -R $RESOURCE_NAME \
-G $RESOURCEGROUP_NAMÈ

# Get the retry interval value from the system defined property
Retry_interval
RETRY_INTERVAL=scha_resource_get -O RETRY_INTERVAL -R $RESOURCE_NAME \
-G $RESOURCEGROUP_NAMÈ

# Obtain the full path for the gettime utility from the 
# RT_basedir property of the resource type.
RT_BASEDIR=scha_resource_get -O RT_basedir -R $RESOURCE_NAME \
-G $RESOURCEGROUP_NAMÈ

# The probe runs in an infinite loop, trying nslookup commands.
# Set up a temporary file for the nslookup replies.
DNSPROBEFILE=/tmp/.$RESOURCE_NAME.probe
probefail=0
retries=0

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 the probe, which queries 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 command comes from the HA-DNS
   # server and not from another name server listed 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

   # If the probefail variable is not set to 0, either the nslookup command
   # timed out or the reply to the query was came from another server
   # (specified in the /etc/resolv.conf file). In either case, the DNS server is
   # not responding and the method calls decide_restart_or_failover,
   # which evaluates whether to restart the data service or to fail it over
   # to another node.

   if [ $probefail -ne 0 ]; then
         decide_restart_or_failover
   else
         logger -p ${SYSLOG_FACILITY}.info -t [$SYSLOG_TAG] \
         “${ARGV0} Probe for resource HA-DNS successful”
   fi
done