WebSphere Application Server for z/OS topology: terminology and system configuration breakdown

Why and when to perform this task

In WebSphere Application Server for z/OS, the functional component on which applications run is called a server. Servers comprise address spaces that actually run code.

Server construction

Within each server are two kinds of address spaces: controllers and servants. A controller runs system authorized programs and manages tasks, such as communication, for the server. Each server has one controller that you start with a JCL start procedure when you enter the appropriate start command on the MVS console.

A servant is the address space in which the JVM resides. It runs unauthorized programs such as business applications. Depending on the workload, a server has one or more servants running at a time. When work builds up, WLM dynamically starts additional servants to meet the demand.

Note: The location service daemon, node agent and JMS server are specialized servers and have no servants.

Here is a quick breakdown of the different server types on your system:

Unmanaged (base) Application Server
The Application Server that was set up during base configuration that hosts your J2EE applications.
Managed (Network Deployment) Application Server
The Application Server set up during Network Deployment configuration that hosts your J2EE applications.
Location service daemon
A server which is the initial point of contact for client requests in either configuration.
JMS server
Hosts the JMS function in the WebSphere Application Server for z/OS, which controls the MQ broker and queue manager in either configuration.
Deployment manager
A specialized Application Server that hosts the administrative console application (it hosts only administrative applications) and provides cell-level administrative function in a Network Deployment configuration. The administrative console application administers servers (grouped into nodes) on many different systems. The deployment manager is the sole occupant of its own node structure which does not need a node agent because there are no Application Servers in the node, and a cell may have only one deployment manager.

Note: The version of the administrative console application that runs in the deployment manager is designed to manage multinode environments, whereas the version in the base Application Server is for single node environments only.

Node agent
Provides node-level administrative function in a Network Deployment configuration.

Note: Every element of the configuration (servers, clusters, nodes and cells) has both a long and short name:

A cluster is a logical grouping of like-configured servers. Clusters exist to promote scalability and availability; workload balancing occurs across the servers in a cluster. Clusters allow you to partition workloads into separate servers while still referring to them as a single unit. Clustering is typically applied to a multinode cell, where each node is configured on a separate system and the cluster has a member (server) on each node. Client requests are distributed among the cluster members based on workload manager decisions.

Note: If you intend for your cluster to span multiple systems in a sysplex, you might need to set up a shared HFS. See "Considerations for clustered servers and stateful session beans" for a list of conditions that would make a shared HFS necessary.

A node contains servers which may be part of a cluster. The cluster may span nodes as long as all involved nodes are in the same cell.

Here is a quick breakdown of clusters, nodes and cells:

cluster
A logical collection of like-configured servers. A cluster can span nodes and systems within the same cell.
node
A logical collection of managed servers on a particular system in the cell. A node can contain servers that are part of clusters that span other nodes, but the node itself is confined to a single system and a single cell. You may configure multiple nodes on the same system--either in the same cell or in different cells. Nodes exist mainly for the purposes of administration, and each Application Server node managed by a deployment manager must have a node agent.
cell
A logical collection of nodes and the boundary of the administrative domain. The nodes that comprise a cell must be configured on systems in the same sysplex. You may configure multiple cells in the same sysplex. Different cells may have nodes on the same systems, though a given node can be a member of only one cell. The cell is the largest unit of organization.

To help you understand the interaction between servers, clusters, nodes and cells, here is a diagram depicting various configurations you can set up in your Network Deployment sysplex:

Configurations of WebSphere Application Server for z/OS

Cells 1 and 3 in the illustration depict Network Deployment configuration cells. Cell 2 is a base configuration cell.


Related concepts
Single server topology
Related reference
WebSphere Application Server for z/OS run-time HFS



Searchable topic ID:   tinstermconfig
Last updated: Jun 21, 2007 9:56:50 PM CDT    WebSphere Application Server for z/OS, Version 5.0.2
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