For many applications, specifically network-aware applications, the hostname on which the application listens and services customer requests must be passed to the application on the command line. Therefore, in many cases, hostname is a parameter you must specify for start, stop, and probe commands for the target resource type (on the Configure screen). However, the hostname on which an application listens is cluster specific—it is determined when the resource is run on a cluster and cannot be determined when Agent Builder generates your resource type code.
To solve this problem, Agent Builder provides the $hostnames variable that you can specify on the command line for the start, stop, and probe commands. You specify the $hostnames variable exactly as you would an actual hostname, for example,
/opt/network_aware/echo_server -p port_no -l $hostnames
When a resource of the target resource type is run on a cluster, the LogicalHostname or SharedAddress hostname configured for that resource (in the Network_resources_used resource property of the resource) is substituted for the value of the $hostnames variable.
If you configure the Network_resources_used property with multiple hostnames, the $hostnames variable contains all of them separated by commas.