The objective of any high availability configuration is to eliminate
all single points of failure (SPOFs).
Figure 1. WebSphere Application Server for z/OS High
Availability Configuration.
This figure illustrates the recommended
WebSphere Application Server for z/OS configuration for high availability.
The key elements are described in the text that accompanies this figure.

Following are the key elements of a WebSphere Application Server for z/OS
high availability configuration:
- Network path redundancy leading up to the Web servers and Applications
Servers.
- Redundant Web servers. (There must be at least two logical partitions
(LPARs) in a high availability sysplex configuration.)
- A highly available sysplex configuration. These LPARs should be on separate
hardware instances to eliminate hardware and software Single Points of Failures
(SPOFs).
- A WebSphere Application Server for z/OS node on each LPAR that is configured
into a Network Deployment cell. The deployment manager server (required, and
configured on its own node ) can be configured on either LPAR or on a separate
LPAR. (The deployment manager server is not depicted in the preceding figure.)
Also note, there is a daemon process (WebSphere CORBA Location Service) on
each LPAR that has one or more nodes in the same cell.
- An application server defined on each node, and formed into a server cluster
with the other application servers in the network.
- A dynamic virtual IP address (DVIPA) defined through the z/OS Sysplex
Distributor as the daemon IP name for the cell. This IP address enables WLM-balanced
routing and fail over between the LPARs for IIOP requests.
- A dynamic virtual IP address (DVIPA) defined through Sysplex Distributor
as the HTTP transport name for the cell. This IP address enables WLM-balanced
routing and fail over between the LPARs for sessionless HTTP requests.
- A static IP address is required for each node as an auxiliary HTTP transport
name for the cell. This enables directed HTTP routing for sessional HTTP requests.
- A WebSphere Web server plug-in must be installed in each of the Web servers
and configured to use the HTTP DVIPA for sessionless requests, and the static
IP addresses for sessional requests.
- If using HTTP sessions, session state must be shared between cluster member
using the data replication service (DRS) or session data must be stored in
DB2. If you are using stateful session Enterprise JavaBeans, the stateful
session persistent store must be configured on a shared HFS. (Using stateful
session Enterprise JavaBeans is not a best practice.)