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Cluster vs load balancing (windows 2008 and SQL 2008)

Posted on 2008-10-08
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I am quite confused between the service cluster and the load balancing.  Is there any pro of Cluster over the load balancing since as I know actually load balancing can do cluster also?  E.g I have 3 machines with load balancing  A, B, C.  If  B machine is down,  the clients still switch to A or C which is the cluster purpose and provide high availability. I don't understand why need service cluster since it is active-passive only. I  think it is just used in several different resources sharing in different machines environment. or application does not  support load balancing.

Is there any called load-balanced cluster? Does it combine  service cluster and load balancing or it is a type of load-balancing only? But really don't understand the pro of combining 2 services

Another question is MS SQL 2008 supports load balancing? If so, SQL 2008 has specify setting to set the load balancing or just replication? No need to set the NLB in 2008?



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Question by:Torus
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chapmandew earned 100 total points
ID: 22668771
SQL Server does not support load balancing natively.  You can design your application so that it does, but it is at the design level, rather than at the sql software level.
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by:deroyer
deroyer earned 100 total points
ID: 22669005
Alright, there needs to be a little bit more understanding of the definitons to fully grasp this concept and the previous expert comment, while correct, may mislead you a little bit.  

Both clustering and load balancing are high availability solutions.  Load balancing can exist without clustering but clustering cannot exist without a virtual name *Similar to load balancing"

In windows, clustering is done at the windows server level (enterprise or above).  The cluster serice is installed on several nodes in (Active/Active Active/Passive, etc.)  The virtual IP addfress (VIP) of the cluster correlates to a load balanced DNS name that points to the active nodes of the cluster.  Chapmandew was correct that an application must be written cluster aware in order for it to function on the cluster.  Because it has to be designed to be able to recognize that this node or that node is the active resource (DB, App, etc)

Now an example of a load balanced solution would be a web server.  I will use Verizon FIOS TV for example to illustrate.  The TV service connects to a load balanced IP address that shares the load to one of over a dozen application web servers in a particular service region by pointing to each server and using the one that responds back the fastest.  If one goes down it isn't a major issue as there are many others that will pickup the load.  Now each application connects to a clustered Active/Passive SQL database server to process its workflow requests.  They connect through the Virtual IP of the cluster node which lists the active node.

As for pro's and con's as you can see there too many variables dependent upon the application and purpise... Help this helps a little bit.  


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by:Torus
ID: 22669145
Well. I understand that the both NLB and cluster service uses same mechanism virtual IP to connect to the server.  But really don't understand if I use IIS which supports load balancing, it is no reason to use cluster since load balancing includes failover part.  And as I said in my question, I just find that the only reason to use cluster because the software doesn't support LB or  different resources across different machines forms a cluster to provide transparent to user to access the resources

Also what is load balanced cluster?
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by:deroyer
ID: 22669441
A load balanced cluster can either be just a fancy way of saying cluster or you can with some apps create VIPs that point to cluster VIPS and have multiple clusters.  What I mean is that technically you could create a cluster of clusters if you were so inclinded, but I have never done it.

As far as this statement goes the primary thing is to have redundancy where posible...  If you have multiple web application servers that all connect to SQL then either could be a viable option.  It really is just a matter of symantecs at that point...
"But really don't understand if I use IIS which supports load balancing, it is no reason to use cluster since load balancing includes failover part.  And as I said in my question, I just find that the only reason to use cluster because the software doesn't support LB or  different resources across different machines forms a cluster to provide transparent to user to access the resources"
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by:Torus
ID: 22669817
Sorry, after your explanation, I still can't got that why use cluster if an application supports load balancing or the using nature is totally different?

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Expert Comment

by:deroyer
ID: 22671425
OK Cluster fails over...  Load balancing spreads the load...
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