When you use sysplex distributor to provide load balancing of tier 1 work requests to DataPower®, and DataPower connects to tier 2 servers on z/OS® in a multisite environment, you can enhance the load balancing configuration by using the multi-tier support of sysplex distributor in combination with load balancing to DataPower.
In figure Figure 1, DataPower is the tier 1 server layer and z/OS applications are the tier 2 servers.
In a multisite environment, each tier 2 sysplex distributor is configured to balance and route service requests to z/OS server application instances in its CPC. The tier 2 distributors send the combined WLM weight of the group of target application instances in their CPC to the tier 1 distributor. The tier 1 distributor makes its load balancing decision using composite weights that are based on the weight received from each tier 1 DataPower target along with the combined WLM weights of the corresponding tier 2 distribution targets.
For example, in figure Figure 1, for DataPower DATAP1 and DATAP2, the weights of CICS1 and CICS2 are included in the tier 1 sysplex distributor decision. For DataPower DATAP3 and DATAP4, the weights of CICS3 and CICS4 are included in the tier 1 sysplex distributor decision.
The tier 1 distribution method that is being used is target controlled (DISTMETHOD TARGCONTROLLED), so each DataPower target sends a weight to the tier 1 distributor that represents its overall health. Because the tier 2 DVIPAs are configured with the CPCSCOPE keyword, their targets must be in the same CPC; the tier 2 distributors aggregate the WLM weights for their GROUP1 target application instances and send the result to the tier 1 distributor. The tier 1 distributor then determines a composite weight for each target based on the DataPower weight and the corresponding tier 2 combined weight.
A CPC is associated with a specific set of DataPower appliances through the use of a shared IPv4 subnet. In figure Figure 1, the DataPower appliances in site 1 are attached to subnet 201.81.10.0/24, and the DataPower appliances in site 2 are attached to subnet 201.81.20.0/24. The CPC in site 1 (CPC1) uses a CPCSCOPE DVIPA that belongs to the site 1 DataPower subnet, 201.81.10.7, and the CPC in site 2 (CPC2) uses another CPCSCOPE DVIPA that belongs to the site 2 DataPower subnet, 201.81.20.7. When the tier 1 sysplex distributor matches DataPower destination IP addresses to tier 2 targets, it uses these CPCSCOPE DVIPAs to determine which z/OS LPARs are associated with which DataPower appliances. OMPROUTE should be set up to advertise host routes for only these CPCSCOPE DVIPA addresses.
The main connection flows in this scenario are the following flows:
- The remote client sends a connection request to the tier 1 sysplex distributor. The tier 1 sysplex distributor collects weights from the available tier 1 DataPower appliances and WLM weights from the available tier 2 servers, creates a composite weight, and determines which DataPower appliance is the best choice for this connection. Sysplex distributor connection routing forwards the inbound packets using GRE to the chosen DataPower appliance.
- DataPower processes the requests and initiates a tier 2 connection. DataPower appliances in site 1 are set up to connect to address 10.81.1.1, while DataPower appliances in site 2 are set up to connect to address 10.81.2.2. The connection request arrives at the appropriate site-local tier 2 sysplex distributor, and a suitable tier 2 server instance is chosen. Responses from the chosen CICS® server instance are routed directly back to the initiating DataPower appliance. When DataPower has finished processing the response from CICS, its response back to the remote client is routed directly back to that client.