WLM even distribution of HTTP requests

(ZOS) Configure an application server to use the WLM even distribution of HTTP requests function

By configuring the application server to use the WLM even distribution of HTTP requests function, HTTP session objects can be evenly distributed by workload management (WLM) to the servants in the configuration. Use this task to distribute HTTP session objects in a round-robin manner among several servants instead of the normal situation where there is a servant affinity, and HTTP session objects reside in one or two servants.

The application server should be running on a z/OS system that is at Version 1.4 or later. Because we are distributing HTTP requests among multiple servants in this task, we should also have multiple servants enabled to use this function. See the topic about enabling multiple servants on z/OS for more information.

Use this task if the application server is experiencing problems with the default workload distribution strategy. The default workload distribution strategy uses a hot servant for running requests that create HTTP session objects. Consider configuring the product and the z/OS Workload Manager to distribute the HTTP session objects in a round-robin manner in the following conditions:

HTTP session objects in memory are used, causing dispatching affinities.
The HTTP sessions in memory last for many hours or days.
A large number of clients with HTTP session objects must be kept in memory.
The loss of a session object is disruptive to the client or server.
There is a large amount of time between requests that create HTTP sessions.
For more background about when to use this task, see the information about WLM even distribution of HTTP requests.

Tasks
In the administrative console, set the WLMStatefulSession property to true.

Expand Servers > Server Types and click WebSphere application servers.
Click the name of the server to use the WLM even distribution of HTTP requests function.
Under Server Infrastructure, expand Administration and click Administration services.
Under Additional properties, click Custom properties.
Click WLMStatefulSession and change the value in the Value field to true if it is currently set to false. If the custom property does not exist, click New, add WLMStatefulSession to the Name field, and add true to the Value field.
Click Apply and then click Save to save the changes to the master configuration.

Set the optimal minimum and maximum number of servants for the workload. Set the minimum and maximum number of servants to handle the expected number of HTTP sessions with affinity. The minimum number of servants should be greater than one. If, for example, you expect 15,000 HTTP session objects are established in the server during the day, then we might set the minimum number of servants to some value larger than one. The minimum of servants is dependent upon the size and number of the HTTP session objects. However, the initial arrival rate of client requests establishing the affinity, the frequency of client interaction, the duration of each client interaction (CPU time and thread occupancy time), and the length of time that the HTTP session object is maintained also need to be considered when establishing the minimum value for the number of servants.

To set the number of servants, click...
Servers > Server Types > WebSphere application servers server Server instance.
Set the minimum and maximum number of servants.
Click Save and synchronize to apply the changes.
If we use a classification mapping file instead of a common workload classification document, and we specify more than one transaction class on a mapping rule for the managed round-robin support that WAS v9 provides, we should remove this section from your classification mapping file. We should use a common workload classification document instead of a classification mapping file because support for the classification mapping file is deprecated. However if we use a classification mapping file, and that file contains a line similar to the following:
TransClassMap *:8080 /Dynacache1Web1/Servlet1 TCLASS1 TCLASS2 TCLASS3
Modify this line such that it specifies only one transaction class. For example, we might change the preceding line to the following line:
TransClassMap *:8080 /Dynacache1Web1/Servlet1 TCLASS1
We also must update the z/OS workload manager policy to remove the extra service classes that are only required fi we want to use the managed round-robin support that WAS v9 provides. Following is an example of how to remove the extra service classes:
  Subsystem-Type  Xref  Notes  Options  Help                                 
 --------------------------------------------------------------------------   
                  Modify Rules for the Subsystem Type     Row 9 to 16 of 16   
 Command ===> ____________________________________________ SCROLL ===> CSR    
                                                                              
 Subsystem Type . : CB          Fold qualifier names?   Y  (Y or N)           
 Description  . . . Component Broker requests                                 
                                                                              
 Action codes:   A=After     C=Copy        M=Move     I=Insert rule           
                 B=Before    D=Delete row  R=Repeat   IS=Insert Sub-rule      
                                                              More ===>       
           --------Qualifier--------               -------Class--------       
 Action    Type       Name     Start                Service     Report        
                                          DEFAULTS: AZAMS1      RBBDEFLT      
  ____  1  CN         AZSR01   ___                  AZAMS1      RAZAMS1       
  ____  2    TC         TCLASS1  ___                AZAMS1      RAZAMS1       
  _d__  2    TC         TCLASS2  ___                AZAMS2      RAZAMS1       
  _d__  2    TC         TCLASS3  ___                AZAMS3      RAZAMS1       
  ____  1  CN         AZSR02   ___                  AZAMS2      RAZAMS2       
  ____  1  CN         AZSR02   ___                  AZAMS3      RAZAMS3       
****************************** BOTTOM OF DATA ****************************** 
Restart the server. The server recognizes the WLMStatefulSession property after it is restarted.
The application server uses the WLM even distribution of HTTP requests function to handle its workload instead of showing affinity to a certain servant.

What to do next
See the topic about detecting and handling problems with runtime components for information on how to handle problems with server clusters and workloads.

Subtopics

WLM even distribution of HTTP requests
The z/OS workload management (WLM) component supports distributing incoming HTTP requests without servant affinity in a round robin manner across the servants. This functionality is intended for, but not limited to long lasting HTTP session objects that are maintained in memory, stateless session EJB, and the create method for stateful session enterprise beans. We can configure the product to use this functionality to spread HTTP requests among active servants that are currently bound to the same work queue as the inbound requests.

Enable multiple servants on z/OS
Detecting and handling problems with runtime components