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What is a Cluster?

There are many types of clusters. The one I am going to cover in this post is a Web cluster. In other words, it is a cluster of several servers built to serve Web pages. It is a made up of Web servers, database servers, and file servers. You may ask, why not deploy only one server and install the Web, database, and file server? There comes a time when one single server cannot sustain the increase in traffic. The high number of visitors exceeds the capacity of the server. Be it processor power, memory availability, disk IOPS, or network IO.

Cluster

Cluster

Building clusters is not for everyone. It is a complex engineering task. The complexity resides in making the whole, called cluster, accomplish the tasks efficiently and seamlessly. It becomes even more complex when one implements load balancing and database replication. Load balancing is the act of distributing tasks across two or more server with identical configurations. Database replication is the synchronization of database tables and meta data across two or more servers. Having two identical databases scales out well especially when it has been designated as the bottleneck.

Advanced Cluster

Advanced Cluster

Too often I get asked, why not deploy a monster server with 32 cores and 64GB of memory instead of building a cluster? While such server might or might not sustain the traffic, there are many points that need to be thought out. The truth is such monster server is cost prohibitive. The price to value is too high and not worth it. The reason being there is currently no commodity server that can handle 32 cores. One would need a considerable budget. For much less, one can get a 32-core cluster. The other point to consider is the fact that the motherboard bus will not be able to sustain the throughput required for a high traffic server. It will not be able to seamlessly pull 64GB/s in and out of the memory system.

Another important point is disaster recovery, one would need another equally powerful server or a very aggressive (read extremely expensive) part-replacement contract. On the other hand, commodity hardware is so affordable one could keep a few spares without breaking the bank! Plus, a monster server will never handle Digg or Slashdot effects. The cluster, however, can scale to accommodate for traffic spikes.

Keep in mind that UNIXy builds clusters for current customers free of charge. The support and service is included with your purchased dedicated servers. Contact us today and we will go above and beyond to help out.

That’s all folks!

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