Start Method

The Start callback method of a resource type implementation is called by the RGM on a chosen cluster node or zone to start the resource. The resource group name, the resource name, and resource type name are passed on the command line. The Start method performs the actions that are needed to start a data service resource in the cluster node or zone. Typically this involves retrieving the resource properties, locating the application specific executable file, configuration files, or both, and starting the application with the correct command-line arguments.

With the DSDL, the resource configuration is already retrieved by the scds_initialize() utility. The startup action for the application can be contained in a function svc_start(). Another function, svc_wait(), can be called to verify that the application actually starts. The simplified code for the Start method is as follows:

int
main(int argc, char *argv[])
{
   scds_handle_t handle;

   if (scds_initialize(&handle, argc, argv)!= SCHA_ERR_NOERR) {
   return (1);   /* Initialization Error */
   }
   if (svc_validate(handle) != 0) {
   return (1);   /* Invalid settings */
   }
   if (svc_start(handle) != 0) {
   return (1);   /* Start failed */
   }
   return (svc_wait(handle));
}

This start method implementation calls svc_validate() to validate the resource configuration. If it fails, either the resource configuration and application configuration do not match or there is currently a problem on this cluster node or zone with regard to the system. For example, a cluster file system that is needed by the resource might currently not be available on this cluster node or zone. In this case, it is futile to attempt to start the resource on this cluster node or zone. It is better to let the RGM attempt to start the resource on a different node or zone.

Note, however, that the preceding statement assumes that svc_validate() is sufficiently conservative, checking only for resources on the cluster node or zone that are required by the application. Otherwise, the resource might fail to start on all cluster nodes or zones and thus enter a START_FAILED state. See the Sun Cluster Data Services Planning and Administration Guide for Solaris OS for an explanation of this state.

The svc_start() function must return 0 for a successful startup of the resource on the node or zone. If the startup function encounters a problem, it must return nonzero. Upon failure of this function, the RGM attempts to start the resource on a different cluster node or zone.

To take advantage of the DSDL as much as possible, the svc_start() function can call the scds_pmf_start() utility to start the application under the Process Monitor Facility (PMF). This utility also uses the failure callback action feature of the PMF to detect process failure. See the description of the -a action argument in the pmfadm(1M) man page for more information.