This section provides some tips about when to use the Start and Stop methods versus using the Prenet_start and Postnet_stop methods. You must have in-depth knowledge of both the client and the data service's client-server networking protocol to decide which methods are appropriate.
Services that use network address resources might require that start or stop steps be done in a certain order relative to the logical hostname address configuration. The optional callback methods Prenet_start and Postnet_stop allow a resource type implementation to do special start-up and shutdown actions before and after network addresses in the same resource group are configured up or configured down.
The RGM calls methods that plumb (but do not configure up) the network addresses before calling the data service's Prenet_start method. The RGM calls methods that unplumb the network addresses after calling the data service's Postnet_stop methods. The sequence is as follows when the RGM takes a resource group online.
Plumb network addresses.
Call data service's Prenet_start method (if any).
Configure network addresses up.
Call data service's Start method (if any).
The reverse happens when the RGM takes a resource group offline:
Call data service's Stop method (if any).
Configure network addresses down.
Call data service's Postnet_stop method (if any).
Unplumb network addresses.
When deciding whether to use the Start, Stop, Prenet_start, or Postnet_stop methods, first consider the server side. When bringing online a resource group containing both data service application resources and network address resources, the RGM calls methods to configure up the network addresses before it calls the data service resource Start methods. Therefore, if a data service requires network addresses to be configured up at the time it starts, use the Start method to start the data service.
Likewise, when bringing offline a resource group that contains both data service resources and network address resources, the RGM calls methods to configure down the network addresses after it calls the data service resource Stop methods. Therefore, if a data service requires network addresses to be configured up at the time it stops, use the Stop method to stop the data service.
For example, to start or stop a data service, you might have to invoke the data service's administrative utilities or libraries. Sometimes, the data service has administrative utilities or libraries that use a client-server networking interface to perform the administration. That is, an administrative utility makes a call to the server daemon, so the network address might need to be up to use the administrative utility or library. Use the Start and Stop methods in this scenario.
If the data service requires that the network addresses be configured down at the time it starts and stops, use the Prenet_start and Postnet_stop methods to start and stop the data service. Consider whether your client software will respond differently depending on whether the network address or the data service comes online first after a cluster reconfiguration, scha_control giveover, or scswitch switchover. For example, the client implementation might do minimal retries, giving up soon after determining that the data service port is not available.
If the data service does not require the network address to be configured up when it starts, start it before the network interface is configured up. This ensures that the data service is able to respond immediately to client requests as soon as the network address has been configured up, and clients are less likely to stop retrying. In this scenario, use the Prenet_start method rather than the Start method to start the data service.
If you use the Postnet_stop method, the data service resource is still up at the point the network address is configured to be down. Only after the network address is configured down is the Postnet_stop method invoked. As a result, the data service's TCP or UDP service port, or its RPC program number, always appears to be available to clients on the network, except when the network address also is not responding.
The decision to use the Start and Stop methods versus the Prenet_start and Postnet_stop methods, or to use both, must take the requirements and behavior of both the server and client into account.