Sysplex distributor extends the notion of dynamic VIPA and automatic VIPA takeover to allow for load distribution among target servers within the sysplex. It extends the capabilities of dynamic VIPAs to enable distribution of incoming TCP connections to ensure high availability of a particular service within the sysplex.
Sysplex distributor supports load balancing to non-z/OS targets. For more information, see Sysplex distribution with DataPower.
The functionality of sysplex distributor is that one IP entity advertises ownership of an IP address by which a particular service is known. In this fashion, the single system image of sysplex distributor is that of a special IP address. This IP address is called a distributed DVIPA. Further, in sysplex distributor, the IP entity advertising the distributed DVIPA and dispatching connections destined for it is itself a system image within the sysplex, referred to as the distributing stack.
Sysplex distributor makes use of Workload Manager (WLM) and its ability to gauge server load and provide a WLM recommendation. In this paradigm, WLM provides the distributing stack with a WLM recommendation for each target system (a WLM system weight) , or the target stacks provide the distributing stack with a WLM recommendation for each target server (a WLM server-specific weight). The distributing stack uses this information to optimally distribute incoming connection requests between a set of available servers. Additionally, sysplex distributor has the ability to specify certain policies within the Policy Agent so that it can use QoS information from target stacks to further modify the WLM recommendation. Further, these policies can specify which target stacks are candidates for clients in particular subnetworks.
Sysplex distributor also measures the responsiveness of target servers in accepting new TCP connection setup requests, favoring those servers that are more successfully accepting new requests. For more information, see Target server connection setup responsiveness monitoring.
The Workload Manager weight is a relative value. The WLM system weight is an indication of the target system's capacity for additional work, and the WLM server-specific weight is a more granular indication of the specific target server's capacity for additional work. Higher numbers indicate a target with comparatively greater capacity. The Netstat VDPT/-O display shows these values. WLM system weights are indicated by a B beside the weight, and WLM server-specific weights are indicated by an S beside the weight.
Distribution using WLM system weights is the default distribution method. This can be specified by using the BASEWLM parameter on the VIPADISTRIBUTE statement. Distribution using WLM server-specific weights can be specified by using the SERVERWLM parameter on the VIPADISTRIBUTE statement. If the SERVERWLM parameter is used and all stacks are able to provide WLM server-specific weights for that VIPA/port, WLM server-specific weights are used. Otherwise, WLM system weights are used.