How the Monitor_check Method Works

The RGM calls the Monitor_check method whenever the PROBE method attempts to fail over the resource group that contains the data service to a new node.

This section describes the major pieces of the Monitor_check method for the sample application. This section does not describe functionality that is common to all callback methods, such as the parse_args() function. This section also does not describe using the syslog() function. Common functionality is described in Providing Common Functionality to All Methods.

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

The Monitor_check method must be implemented so that it does not conflict with other methods that are running concurrently.

The Monitor_check method calls the Validate method to verify that the DNS configuration directory is available on the new node. The Confdir extension property points to the DNS configuration directory. Therefore, Monitor_check obtains the path and name for the Validate method and the value of Confdir. It passes this value to Validate, as shown in the following listing.

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

# Obtain the name of the Validate method for this resource.
VALIDATE_METHOD=`scha_resource_get -O Validate \
   -R $RESOURCE_NAME -G $RESOURCEGROUP_NAMÈ

# Obtain the value of the Confdir property in order to start the
# data service. Use the resource name and the resource group entered to
# obtain the Confdir value set at the time of adding the resource.
config_info=`scha_resource_get -O Extension -R $RESOURCE_NAME \
 -G $RESOURCEGROUP_NAME Confdir`

# scha_resource_get returns the type as well as the value for extension
# properties. Use awk to get only the value of the extension property.
CONFIG_DIR=`echo $config_info | awk `{print $2}'`

# Call the validate method so that the dataservice can be failed over
# successfully to the new node.
$RT_BASEDIR/$VALIDATE_METHOD -R $RESOURCE_NAME -G $RESOURCEGROUP_NAME \
   -T $RESOURCETYPE_NAME -x Confdir=$CONFIG_DIR

See How the Validate Method Works to see how the sample application verifies the suitability of a node for hosting the data service.