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

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

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!

Varnish is an excellent Web accelerator that can be made to proxy requests in and out of a cluster of somewhat more fully fledged Web servers like Apache or Litespeed. It has some great features like its compiled language, called VCL, and C-like programming API.

Large vBulletin deployments tend to be heavy on CPU and memory due to PHP script processing. For a large vBulletin forum, we recommend a cluster of 5 physical servers with three of those running Xen virtualization. One of those servers will be dedicated to the MySQL master database. Three to be setup as “headless” PHP nodes and Varnish load balancing and failover. And finally one as the NFS file store. The three headless servers need to run Varnish in their own VM and Litespeed or Apache in their own VM similarly.

The varnish backend director functionality makes it ideal to balance incoming traffic across all PHP headless nodes. It makes the configuration scalable and plug and play especially when needing to scale out within hours. The challenge in this setup is in making Varnish work correctly with vBulletin. Otherwise, session problems will occur.

We have a lot to share on this implementation so keep checking this blog as we will post it all. In the next installment, we’ll go through our deployment of a large vBulletin forum for a customer. In the mean time, feel free to get in touch should you have a question or comment. If you are interested in us helping you accelerate your server, we have a page explaining the different technologies we deploy on our clients’ dedicated servers. Read up here: http://www.unixy.net/accelerate-your-server

Update: we are offering a Varnish configuration for vBulletin (3 & 4) for a one-time fee. We can also configure it free of charge should you decide to rent your fully managed dedicated server from UNIXY (http://www.unixy.net). Please contact us today to get your forum running with a blazing fast speed!

That’s all folks!