9.5. Reloading Services After a Definition Change

The cluster automatically detects changes to the definition of services it manages. However, the normal response is to stop the service (using the old definition) and start it again (with the new definition). This works well, but some services are smart and can be told to use a new set of options without restarting.

To take advantage of this capability, your resource agent must:

Accept the reload operation and perform any required actions.

The steps required here depend completely on your application

Example 9.9. The DRBD Agent's Control logic for Supporting the `reload` Operation


  case $1 in
    start)
	drbd_start
	;;
    stop)
	drbd_stop
	;;
    reload)
	drbd_reload
	;;
    monitor)
	drbd_monitor
	;;
    *)	
	drbd_usage
	exit $OCF_ERR_UNIMPLEMENTED
	;;
  esac
  exit $?

Advertise the reload operation in the actions section of its metadata

Example 9.10. The DRBD Agent Advertising Support for the `reload` Operation


  <?xml version="1.0"?>
  <!DOCTYPE resource-agent SYSTEM "ra-api-1.dtd">
  <resource-agent name="drbd">
    <version>1.1</version>
    
    <longdesc lang="en">
      Master/Slave OCF Resource Agent for DRBD
    </longdesc>
    
    <shortdesc lang="en">
      This resource agent manages a DRBD resource as a master/slave
      resource. DRBD is a shared-nothing replicated storage device.
    </shortdesc>
    
    <parameters>
      <parameter name="drbd_resource" unique="1" required="1">
        <longdesc lang="en">The name of the drbd resource from the drbd.conf file.</longdesc>
        <shortdesc lang="en">drbd resource name</shortdesc>
        <content type="string"/>
      </parameter>
      
      <parameter name="drbdconf" unique="0">
        <longdesc lang="en">Full path to the drbd.conf file.</longdesc>
        <shortdesc lang="en">Path to drbd.conf</shortdesc>
        <content type="string" default="${OCF_RESKEY_drbdconf_default}"/>
      </parameter>
      
    </parameters>
    
    <actions>
      <action name="start"   timeout="240" />
      <action name="reload"  timeout="240" />
      <action name="promote" timeout="90" />
      <action name="demote"  timeout="90" />
      <action name="notify"  timeout="90" />
      <action name="stop"    timeout="100" />
      <action name="meta-data"    timeout="5" />
      <action name="validate-all" timeout="30" />
    </actions>
  </resource-agent>

Advertise one or more parameters that can take effect using reload.

Any parameter with the unique set to 0 is eligable to be used in this way.

Example 9.11. Parameter that can be changed using reload


  <parameter name="drbdconf" unique="0">
    <longdesc lang="en">Full path to the drbd.conf file.</longdesc>
    <shortdesc lang="en">Path to drbd.conf</shortdesc>
    <content type="string" default="${OCF_RESKEY_drbdconf_default}"/>
  </parameter>

Once these requirements are satisfied, the cluster will automatically know to reload, instead of restarting, the resource when a non-unique fields changes.

Note

The metadata is re-read when the resource is started. This may mean that the resource will be restarted the first time, even though you changed a parameter with unique=0

Note

If both a unique and non-unique field is changed simultaneously, the resource will still be restarted.