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After having explained some basic concepts of WebSphere high availability on z/OS, let us put together a sample high availability configuration for z/OS. See Figure 8-10.
Figure 8-10 High availability WebSphere in a sysplex configuration,
This high availability WebSphere configuration on z/OS requires a Parallel Sysplex environment plus the following setups within and outside the Parallel Sysplex.
Setup outside the Parallel Sysplex includes:
- Redundant network path leading to the Web servers and appservers.
- Redundant Web servers. In many cases, HTTP servers are on another platform instead of z/OS while appservers run on z/OS.
- A WebSphere Web server plug-in must be installed in each of the Web servers and configured to use HTTP DVIPA for sessionless requests and static IP addresses for sessional requests.
Setup within the Parallel Sysplex includes:
- A highly available Parallel Sysplex with two Coupling Facilities and at least three LPARs hosting appservers within a cell. The LPARs in the sysplex should be on separate hardware instances to prevent a single point of failure. A high availability configuration without the need to perform software, hardware or application updates only needs two LPARS. We recommend a third LPAR in the configuration such that the configuration is highly available even when one of the LPARs is brought down for upgrade.
- A WAS for z/OS node on each LPAR that is configured into a ND cell. The Deployment Manager server (required, and configured on its own node) can be configured on one of the LPARs or on a separate LPAR. Also note that there is a daemon process (WebSphere CORBA Location Service) on each LPAR that has one or more nodes in the same cell.
- An appserver defined on each node, and formed into a server cluster which consists of at least three nodes from three LPARs.
- 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 failover 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 failover 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.
- If using HTTP sessions, the session state must be shared between the cluster member using DRS or session data must be stored in DB2. If you are using stateful session Enterprise JavaBeans (EJBs), the stateful session must be replicated using DRS, and a shared HFS must be configured for passivating session EJBs. Note that using stateful session beans is not a best practice.
