High-level Architecture

The Architecture is simple once you understand the high-level architecture objects.

Server

In an architectureal context, a Server is a JVM process running WAS. You can very easily set up one WAS instance to have two servers, say server1 and server2. If you ran ps after starting them, you would see two java processes. Each server has its own independent JVM, class loaders, etc. This is why JVM parameters and many performance-related settings are made on the server level.

The default server name is server1.

Node or Instance

A Node or an Instance is a collection of servers housed under a single directory. All the servers of this Node/Instance may be administered through the same wsadmin or Admin Console session. The IBM documentation usually calls the main instance (which has the WAS software installed under the main directory) a Node, and the other instances Configuration Instances. This makes this very simple concept confusing for beginners. Just remember that even though IBM never says it, alternative WAS configuration instances are configured exactly the same as any standalone node. There is no architectural difference other than the location of the WAS software.

Alternate Configuration Instance

An Alternate Instance is just a Node that does not have the WAS software installed under the main directory. Whenever the WAS software is installed, a "main instance" is installed. All other instances are created by running "wsinstance.sh", and are alternative configuration instances. Node names should be unique, whether the node is a main instance or an alternate configuration instance.

Cell

Normally, when you run a wsadmin or Admin Console command, you are sending commands to a Node (aka Instance). If, however, you have a Network Deployment installation, administrative commands can be applied to a a group of nodes called a Cell. A cell is just a grouping, for administrative purposes, of nodes/instances. When doing cell administration, IBM always calls instances "nodes".

The default cell name is the same as your node name.

Cluster

A collecton of servers within a cluster which run as a single, distrubuted unit for load sharing and high availability reasons.