difference between the distribution & cluster?

is there difference between the distribution & cluster?
distribuion mean : we mean RMI, EJB, failover, loadbalancing
but  for the clustering, we mean only failover, loadbalancing aand sever backup

am i all right with the above comments??
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I'm a bit confused by the question by I will explain.  Distribution and clustering are two difference concepts.
Distribution is when you move the different tiers of your application and deploy them to different servers or clusters.
Distribution requires load balancing for method calls to EJBs.  It provides more flexibility for balancing the load between servers that provide HTTP content and servers that provide objects.  it also provides higher availability due to fewer single points of failure.

Clustering is taking the different tiers and replicating the services across servers for better performance and high availbility.   So in a J2EE world you can cluster the HTTP server, web container, and the EJB container.  Clustering provides failover and load balancing.  

To make an robust system you would combine the two.  You would use distribution to spead out your application across clusters providing the services.  Clustering is at a lower level than distribution.  Clustering is a service provided by or for the J2EE server and distribution is logical breakup of an application across tiers.

Hope that helps.


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she1Author Commented:
thanks , but still confusing from your comments.

web container(web server support cluster, it mean same contents backup to different server to support failover, in case of one web server failture, another one can take over the task)

ejb support distribution, it mean different content (object)
located in different server(especially ejb object), so one oject can call another object located in another machine.

is it right?
yes you are right...  
EJBs are location independent; you do not need to know where a bean resides, you just need to be able to connect to a node in the application server, request the bean, and then use it, not knowing its location.  This requires some 'catalog' to tell the server where a bean lives such as a JNDI service.

she1Author Commented:
thanks, how about my following explain is it right?


web container(web server support cluster, it mean same contents backup to different server to support failover, in case of one web server failture, another one can take over the task)

but for wls web container/tomcat, it support RMI, but not EJB.
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