Policy interactions

The Policy Agent interacts with the sysplex distributor to assist with workload balancing. There will be one Policy Agent running on an LPAR regardless of how many stacks are configured. First, the Policy Agent can be configured to collect network performance statistics for applications being distributed on target stacks. These network performance statistics are then used to modify the overall WLM weight assigned to a target server. In this way, processor performance, server performance, and application network performance are taken into account when distributing work. Second, policies established on the distributing stack can be configured to restrict the set of target stacks to be considered for any given inbound connection request. In this way, the total set of target stacks can be partitioned among different groups of users or applications requesting connections to distributed applications.

Previously, the QoS performance data was collected by the Policy Agent on the target for each DVIPA and port or application. After collecting the QoS information, the Policy Agent on the target stack pushed this information down to the stack sysplex function which then forwarded it to the stack sysplex function on the distributing stack. There are two significant additions to Policy Agent and sysplex interaction:

The Policy Agent at each target will collect information with an additional level of granularity; the QoS performance data will be collected for each service level that a target's DVIPA port or application supports.
The Policy Agent on the distributing stack drives the collection of this information by pulling it from the Policy Agents on the target stacks:
- The Policy Agent on the distributor opens up one or two TCP connections to each of the Policy Agents on the target stacks. The distributor can be configured to distribute connections to IPv4 DVIPAs, IPv6 DVIPAs, or both. The Policy Agent opens an IPv4 connection to a target stack's IPv4 XCF address if it is configured to distribute to an IPv4 DVIPA on that target, and likewise opens an IPv6 connection to a target stack's IPv6 XCF address if it is configured to distribute to an IPv6 DVIPA on that target. As a result, if the routing stack is distributing connections to both IPv4 and IPv6 DVIPAs on a given target, then two connections to that target are opened.
  For more information on how the sysplex distributor determines its targets, see Configuring distributed DVIPAs — sysplex distributor.
- The Policy Agent on the distributing stack will send across a list of QoS service level names to the Policy Agent on each target.
- The Policy Agent on each target will send back a QoS Policy Action weight fraction for each requested service level that each target DVIPA port/application supports. A specific Policy Action weight fraction will not be sent unless the distributing stack's Policy Agent requests it. Only weight fractions for IPv4 DVIPA ports and applications flow on the IPv4 Policy Agent connection, and similarly, only IPv6 weight fractions flow on the IPv6 Policy Agent connection.
- Upon receiving the QoS Policy Action weight fraction, the Policy Agent on the distributing stack will pass this information down to the sysplex distribution function on the stack. If two connections to a given target Policy Agent are active, weight fractions for IPv4 DVIPA ports or applications and IPv6 DVIPA ports or applications are passed to the sysplex distribution function separately. The stack sysplex distribution function uses this additional information when it is selecting targets for incoming connections. If it does not have a QoS Policy Action weight fraction, then it uses the existing weight fraction to make the load distribution decision instead.