Configuring the multiple application-instance scenario

For the multiple application-instance scenario, each instance is assigned a unique DVIPA. The VIPADEFINE keyword of the VIPADYNAMIC configuration statement is used to create the DVIPA on the stack where the DVIPA is normally expected to be active. When the VIPADEFINE statement is processed in a TCP/IP profile, corresponding DEVICE, LINK, HOME, and BSDROUTINGPARMS statements are generated automatically for IPv4 addresses. For IPv6 addresses, an INTERFACE statement is automatically generated. Routing daemons are automatically informed.

Additional configuration is required on other stacks in the sysplex to indicate which stack should take over the DVIPA in the event of a failure. The VIPADYNAMIC statement has a VIPABACKUP keyword for this purpose. A VIPABACKUP configures the DVIPA but does not activate it until it is necessary. Because more than one TCP/IP can back up a single DVIPA, a rank parameter on the VIPABACKUP statement determines the order in which several stacks will assume responsibility for a DVIPA.

The stacks in the sysplex exchange information on all VIPADEFINEs and VIPABACKUPs defined in the sysplex, so that all are aware of which stack should take over a particular DVIPA. The list of backup stacks for a specific DVIPA can be different from the list of backup stacks for all other DVIPAs.

In the multiple application-instance scenario, instances of the application in question are activated among sysplex nodes according to some plan, presumably related to balancing workload across available capacity. This activation is done independently of VIPA takeover. Configure the associated DVIPAs as follows:

1. For each instance of a particular application to be supported via DVIPA, add a VIPADEFINE statement to the TCP/IP profile for the TCP/IP associated with the application instance.
2. For each of the dynamic VIPAs in step 1, determine which application instance or instances should take over the workload (considering probable capacity and any other application-related considerations). If more than one TCP/IP is to provide backup for a DVIPA, determine the order in which the selected TCP/IPs should be designated as backup. Add a VIPABACKUP statement to each TCP/IP that is to provide backup for the DVIPA, with appropriate rank values to determine the order. Do this for each of the DVIPAs in step 1.
3. Perform steps 1 and 2 for each other application to be supported by DVIPAs.
   Note: It is possible to share a dynamic VIPA among several different applications, but in doing so, ensure that instances of all such applications will exist together on any TCP/IP to which the DVIPA may be moved in case of a failure.

After these steps are complete, start the affected TCP/IPs (or modify their configuration using the VARY TCPIP,,OBEYFILE command), if applicable, configure DNS for the application names, and start the application instances. From that point on, the TCP/IPs in the sysplex will collaborate to ensure that each dynamic VIPA is kept active somewhere within the sysplex as long as there is at least one functioning TCP/IP which has been designated as backup for the dynamic VIPA.

Note: The limit of 1024 DVIPAs on a single TCPIP applies to the DVIPAs that are defined by the VIPADEFINE or VIPABACKUP configuration statements or by a VIPADISTRIBUTE statement on another stack.