Date Created: Mon 23-Mar-2009

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    WebSphere Cluster versus Load Balance

    Question:
    I want to know what's the differences between using a WebSphere Application Server cluster and load balance? cluster consists of load balance?


    Basic Answer:
    When we talk about scalability and Workload Management (WLM) then cluster comes to picture. A WebSphere cluster consists of having multiple application servers (cluster member or clones) across a machine (Vertical Cluster) or across several machines (Horizontal Cluster).

    When looking a a clustered web application deployed to a single cluster we can say the application is load balanced as long as we use IBM HTTP Server (IHS) to provide workload management via a plugin. When WLM is enabled by using IHS the client HTTP requests are distributed across the application servers by configured web server definitions in the administration console and mapping of application to these server.

    Clustering without IHS WLM still allows for high availability and workload management for all other protocols like RMI etc. This is dependant on the design of the Enterprise application. Bad programming can invalidate a cluster design. It is all about how IIOP is used or CorbaLoc.

    There are several modes of load balancing using software i.e. handled using WebSphere plugin, which we can call HTTP WLM and cluster load balance for other Java protocols i.e RMI and we can also use the IBM Edge server software which can become a software load balancer which sprays IP traffic to IHS (if web WLM is being used) or spray IP traffic to WAS Clusters. Remember the application design must be design correctly to benefit the clustering model. You can also use a hardware load balancer such as Nortel Application Switches e.g Alteon.

    Below is a diagram that shows a simple diagram of what we mean by vertical and horizontal clusters.



    You will notice in this diagram that the Deployment Manager is on the same node as Node 01, but this doesn't have to be the case. Often it is because of budget constraints and ease of use. in this diagram IBM HTTP Server (IHS) is also installed on the same node as Node 01, but could be separate machine. If IHS is not on the same machine as a WebSphere node it makes administration and maintenance more complex. A physical Load Balancer would exist between the client and the web server.

    An example of a possible Load balanced Workload Management (WLM) design is shown below.



    The diagram above depicts a possible configuration for load balancing and workload management for IBM WebSphere Network Deployment  (ND). The load balancers could be appliances or software. IHS (IBM HTTP Server) is used for workload management to spray HTTP requests in a round robin fashion across the applications on clones. The WebSphere Plug-in is used by IHS and allows requests to spray across application clones in a cluster.


    You can download this presentation if you wish?

    WebSphere_LoadBalance_WorkloadManagement.ppt

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Steve Robinson - IBM Champion 2013

About Me

Steve Robinson has been working in IT for over 20 years and has provided solutions for many large-enterprise corporate companies across the world. Steve specialises in Java and Middleware.

In January 2013, I was awarded the prestigous 'IBM Champion' accolade.


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IBM WebSphere Application Server 8.0 Administration Guide

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