TCP/IP load balancing

Load balancing ensures high system availability through the distribution of workload across multiple components.

TCP/IP load balancing provides high availability of the Gateway daemon by distributing connections from clients across multiple Gateway daemons. The efficiency of load balancing can also be increased by taking into account CICS® server status provided by dynamic feedback to the IBM® z/OS® Workload Manager (WLM).

When TCP/IP load balancing is being used, a connection request from a Client application is received through a network socket by the TCP/IP load balancing component. This component decides which Gateway daemon in the Gateway group receives the request. A connection is established to the chosen Gateway and, when it is established, requests from the Client application continue to go through the same connection to the chosen Gateway daemon. The Client application cannot determine which Gateway daemon instance is selected.

If a problem occurs, such as a temporary network failure, or an unplanned shutdown of CICS Transaction Gateway or IBM WebSphere® Application Server, the existing connection is lost. The next time a request is received, a new connection is created. This connection can go to any Gateway daemon instance in the Gateway group.

An IPIC connection between CICS Transaction Gateway and a CICS server must not be load balanced through any TCP/IP port sharing or load balancing software.

To support TCP/IP load balancing for XA requests a highly available Gateway group (HA group) must be defined. For more information, see Highly available Gateway group.

The use of the APPLID qualifier has implications for CICS connections. For more information, see IPIC server connectionsIPIC server connections.