WebSphere Concepts: Cell, Node, Cluster, Server…

Quick post… If you are not familiar with WebSphere at first you might get confused with its concepts: cell, deployment manager, node, node agent, cluster, server, …

First of all, lets start with the concept of a Cell:

A Cell is a virtual unit that is built of a Deployment Manager and one or more nodes. I guess a picture will help making things clearer:

But still there are a few concepts that need to be explained. The next obvious one is the Deployment Manager.

The Deployment Manager is a process (in fact it is an special WebSphere instance) responsible for managing the installation and maintenance of Applications, Connection Pools and other resources related to a J2EE environment. It is also responsible for centralizing user repositories for application and also for WebSphere authentication and authorization.

The Deployment Manager communicates with the Nodes through another special WebSphere process, the Node Agent.

The Node is another virtual unit that is built of a Node Agent and one or more Server instances.

The Node Agent it the process responsible for spawning and killing server processes and also responsible for configuration synchronization between the Deployment Manager and the Node. Extra care must be taken when changing security configurations for the cell, since communication between Deployment Manager and Node Agent is ciphered and secured when security is enabled, Node Agent needs to have configuration fully resynchronized when impacting changes are made to Cell security configuration.

Servers are regular Java process responsible for serving J2EE requests (eg.: serving JSP/JSF pages, serving EJB calls, consuming JMS queues, etc).

And to finish, Clusters are also virtual units that groups Servers so resources added to the Cluster are propagated to every Server that makes up the cluster, this will in fact affect usually more than a single Node instance.

Lets finish this post with another diagram to illustrate all those concepts.

http://itdevworld.wordpress.com/2009/05/03/websphere-concepts-cell-node-cluster-server/

How does cluster computer work in a network? How do they send message to one another?

Cluster Computer, this technology used to maintain availability of server or computer fully(24 hours, 365 days). For this kind of support they configure the first server then they configure the second server with the same configuration. Both server connected over network(sometime both in geographically different location). The two server having same IP address with clustering software. Also there is additional network card in both computers. This maintained the Heart Beat of cluster server.

Suppose the first computer/server is the main one, whenever the main fails the second one going to be linked.

So the second computer always checks the Heart Beat of first server for each micro seconds, if heart beat fails the second going to be response the request over network.

http://answers.yahoo.com/question/index?qid=20090820022457AADuqmT

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