Routing considerations

You can choose to have work always run in a specified region. This is known as static routing. CICSPlex® SM WLM uses dynamic routing to control where work requests are run. You can implement dynamic routing in a hub model or a distributed model.

Dynamic routing compared to static routing

With static routing, work always runs in a specified region. In a CICSplex or BTS-set, resources such as transactions and programs required in one region might be owned by another. For example, you might have a terminal-owning region (TOR) that requires access to transactions owned by an application-owning region (AOR). If you specify the location of a resource when you design your system (for example, in the installed resource definition) requests of that resource are always routed to the same region.

If you have relatively few CICS® regions, static routing might be appropriate for you. However, there are considerations with specifying an exact SYSID for routing purposes:
  • The route can only be made to the specified SYSID. If that region is unavailable, unresponsive, or unhealthy, this can cause problems.
  • If the SYSID changes, the code that specifies it must also be changed.

With dynamic routing, the decision on where to run a piece of work is made by a dynamic routing program. In CICSPlex SM, the program is a user-replaceable dynamic routing program called EYU9XLOP.

CICSPlex SM WLM dynamic routing is application-agnostic. Values are not coded into the application. It does not require specialist application code to handle different circumstances. It provides flexibility for movement between environments and changes in names in environments. For example, a change in the number of regions can be handled with only a quick change to CICSPlex SM WLM instead of the change to application source code that static routing would require.

What are the roles of CICS regions in dynamic routing?

The CICS regions involved in dynamic routing can act as one or more of the following:
Requesting region
The CICS region where the work request is initiated. For terminal-initiated transactions and for inbound DPL client requests, the requesting region is typically a terminal-owning region (TOR). For EXEC CICS START commands that are associated with a terminal, for peer-to-peer DPL requests, for non-terminal related EXEC CICS START commands, for CICS BTS processes and activities, and for Link3270 bridge requests, the requesting region is typically an AOR.
Routing region
The CICS region that decides where to route the work request. For terminal-initiated transactions and terminal-associated EXEC CICS START commands, for CICS CICS BTS processes and activities, and for Link3270 bridge requests, the routing region is typically an AOR.
Target region
The CICS region where the request is executed. For all dynamically-routed transactions, programs, and BTS processes and activities, the target region is typically an AOR.

A region can be both a routing and a target region.

EYU9XLOP: the CICSPlex SM dynamic routing program

CICSPlex SM WLM uses a user-replaceable dynamic routing program called EYU9XLOP to create the environment necessary for dynamic routing and to set up the CICSPlex SM runtime environment.

For most situations, the supplied workload management capabilities are sufficient. However, if it is ever needed, you can customize the module that drives CICSPlex SM workload management processing. For more information, see Creating a user-replacement module for EYU9WRAM.