Stop Method

The Stop method is invoked on a cluster node when the resource group containing the HA-DNS resource is brought offline on that node or if the resource group is online and the resource is disabled. This method stops the in.named (DNS) daemon on that node.

This section describes the major pieces of the Stop method for the sample application. It does not describe functionality common to all callback methods, such as the parse_args function and obtaining the syslog facility, which are described in Providing Common Functionality to All Methods.

For the complete listing of the Stop method, see Stop Method Code Listing.

Stop Overview

There are two primary considerations when attempting to stop the data service. The first is to provide an orderly shutdown. Sending a SIGTERM signal through pmfadm is the best way to accomplish this.

The second consideration is to ensure that the data service is actually stopped to avoid putting it in Stop_failed state. The best way to accomplish this is to send a SIGKILL signal through pmfadm.

The Stop method in the sample data service takes both these considerations into account. It first sends a SIGTERM signal. If this signal fails to stop the data service, the method sends a SIGKILL signal.

Before attempting to stop DNS, this Stop method verifies that the process is actually running. If the process is running, Stop uses the process monitor facility (pmfadm) to stop it.

This Stop method is guaranteed to be idempotent. Although the RGM should not call a Stop method twice without first starting the data service with a call to its Start method, the could call a Stop method on a resource even though the resource was never started or it died of its own accord. Therefore, this Stop method exits with success even if DNS is not running.

Stopping the Application

The Stop method provides a two-tiered approach to stopping the data service: an orderly or smooth approach using a SIGTERM signal through pmfadm and an abrupt or hard approach using a SIGKILL signal. The Stop method obtains the Stop_timeout value (the amount of time in which the Stop method must return). Stop then allocates 80% of this time to stopping smoothly and 15% to stopping abruptly (5% is reserved), as shown in the following sample.

STOP_TIMEOUT=`scha_resource_get -O STOP_TIMEOUT -R $RESOURCE_NAME
\

-G $RESOURCEGROUP_NAMÈ
((SMOOTH_TIMEOUT=$STOP_TIMEOUT * 80/100))

((HARD_TIMEOUT=$STOP_TIMEOUT * 15/100))

The Stop method uses pmfadm -q to verify that the DNS daemon is running. If it is, Stop first uses pmfadm -s to send a TERM signal to terminate the DNS process. If this signal fails to terminate the process after 80% of the timeout value has expired Stop sends a SIGKILL signal. If this signal also fails to terminate the process within 15% of the timeout value, the method logs an error message and exits with error status.

If pmfadm terminates the process, the method logs a message that the process has stopped and exits with success.

If the DNS process is not running, the method logs a message that it is not running and exits with success anyway. The following code sample shows how Stop uses pmfadm to stop the DNS process.

# See if in.named is running, and if so, kill it. 
if pmfadm -q $PMF_TAG; then 
   # Send a SIGTERM signal to the data service and wait for 80% of
the
   # total timeout value.
   pmfadm -s $RESOURCE_NAME.named -w $SMOOTH_TIMEOUT TERM
   if [ $? -ne 0 ]; then 
      logger -p ${SYSLOG_FACILITY}.err \
          -t [$RESOURCETYPE_NAME,$RESOURCEGROUP_NAME,$RESOURCE_NAME] \
          “${ARGV0} Failed to stop HA-DNS with SIGTERM; Retry with \
           SIGKILL”
      
      # Since the data service did not stop with a SIGTERM signal, use 
      # SIGKILL now and wait for another 15% of the total timeout value.
      pmfadm -s $PMF_TAG -w $HARD_TIMEOUT KILL
      if [ $? -ne 0 ]; then
          logger -p ${SYSLOG_FACILITY}.err \
          -t [$SYSLOG_TAG]
          “${ARGV0} Failed to stop HA-DNS; Exiting UNSUCCESFUL”
          
          exit 1
      fi   
fi
else 
   # The data service is not running as of now. Log a message and 
   # exit success.
   logger -p ${SYSLOG_FACILITY}.err \
           -t [$SYSLOG_TAG] \
           “HA-DNS is not started”

   # Even if HA-DNS is not running, exit success to avoid putting
   # the data service resource in STOP_FAILED State.

   exit 0

fi

# Could successfully stop DNS. Log a message and exit success.
logger -p ${SYSLOG_FACILITY}.err \
    -t [$RESOURCETYPE_NAME,$RESOURCEGROUP_NAME,$RESOURCE_NAME]
\
    “HA-DNS successfully stopped”
exit 0

Stop Exit Status

A Stop method should not exit with success until the underlying application is actually stopped, particularly if other data services have dependencies on it. Failure to do so can result in data corruption.

For a complex application, such as a database, be certain to set the value for the Stop_timeout property in the RTR file sufficiently high to allow time for the application to clean up while stopping.

If this method fails to stop DNS and exits with failure status, the RGM checks the Failover_mode property, which determines how to react. The sample data service does not explicitly set the Failover_mode property, so it has the default value NONE (unless the cluster administrator has overridden the default and specified a different value). In this case, the RGM takes no action other than to set the state of the data service to Stop_failed. User intervention is required to stop the application forcibly and clear the Stop_failed state.