Controlling distribution of work in a network

By modifying WLM's distribution numbers with the policy agent, workload can be shifted according to the overall requirements of the organization.

z/OS can function as a server for thousands of different large scale applications, like CICS, IMS, and all of the well-known IP servers. These applications are often mission-critical and experience workloads in the range of tens of thousands concurrent users. An organization has guidelines for the service level that is appropriate for a given service. (Sometimes, these guidelines are formalized in a service level agreement.)

In such a context, some hosts in the sysplex would best be left with more or less overall workload than others. To this end, the distribution numbers provided by WLM can be modified by the z/OS policy agent. By modifying WLM's numbers with the policy agent, workload can be shifted according to the overall requirements of the organization.

Note: A full description of the policy agent is beyond the scope of this information, but you should know that the policy agent is a z/OS application that influences such networking functions as:

TCP/IP quality of service (TCP session control)
Intrusion detection services (recognition of dangerous IP traffic as it arrives at the z/OS host).
Sysplex distributor.
Packet filtering, Application Transparent - TLS, and Virtual Private Networks.

The policy agent influences these environments based upon explicitly coded policies. These policies can be retrieved from LDAP servers, which can be accessed from a host on the network (allowing a centralized repository of policies shared among all platforms, not just z/OS).

There are other, less complex, methods of controlling the distribution of connections with sysplex distributor. The VIPADISTRIBUTE statement in Figure 1 did not code the distribution method, so the system used the default (DISTMETHOD BASEWLM).

Figure 1. LPAR 1 sample configuration statements

 IPCONFIG SYSPLEXROUTING DYNAMICXCF 192.168.80.1 255.255.255.0
 VIPADYNAMIC
 VIPADEFINE 255.255.255.192 10.134.61.190
 VIPADISTRIBUTE DEFINE SYPLEXPORTS 10.134.61.190 PORT 21 DESTIP ALL
 ENDVIPADYNAMIC

That is, the same effect could have resulted from coding:

Figure 2. Alternative sample configuration statement

VIPADISTRIBUTE DEFINE SYSPLEXPORTS DISTMETHOD BASEWLM 10.134.61.190 PORT 21
DESTIP ALL

The DISTMETHOD BASEWLM option means the distribution method uses WLM. If we change this option to DISTMETHOD ROUNDROBIN, sysplex distributor does not consult the Workload Manager at all. Instead, it does simple round robin distribution: connections are distributed continually to consecutive hosts.

Beginning with z/OS V1R7, sysplex distributor can control distribution based upon finer-grained data from WLM. In particular, sysplex distributor can take into account whether a specific application is meeting its performance goals as defined to WLM and can keep track of the target server's response time. Faster responding servers receive more connections. Instead of coding DISTMETHOD BASEWLM in the sample above, DISTMETHOD SERVERWLM would be used for this.