Clustered website hosting is a type of hosting which involves multiple servers for the same task, and is generally seen as a more reliable type of hosting over standard shared website hosting. With clustered web hosting, all website services are ‘load balanced’ across multiple servers to ensure that the best redundancy possible is achieved; security resources and other standard features are also spread across multiple servers. No human interaction is required for the clustered hosting system to work; this is because most clustered hosting platforms are data driven in some way or another. Most clustered hosting services suffer no downtime because if one server within the cluster fails, there is multiple servers to take over its role; if downtime is ever experienced with clustered website hosting, the reason is normally because there has been a major problem with either the power or the network at the data centre in which the clustered setup - although both instances of fault are very rare. Most clustered setups are normally continually monitored, so if a server does happen to malfunction or face an error of sorts, an on-site network team or support team from the web host will be quickly dispatched to ensure that the problem is fixed quickly and effectively; there are also normally automated systems in place to ensure that the cluster isn’t affected if it is missing a server or two, but in most cases the end-users will not see any problems. Clustered hosting is seen as a solution for businesses and large corporations who require an update percentage which is near to or equals to 100%; this is because although clustered hosting does come at a cost, it is one that is cheaper than a dedicated server - one other thing to note is that the reliability of dedicated servers is not as good as clustered hosting, although some individuals think the opposite.

Virtualization

Clustered hosting could also be seen as a type of virtual website hosting; this is because the actual system is in a sense ‘virtualized’ because of the number of servers that are clustered together. To ensure reliability, and to allow clustered website hosting to achieve its job, websites and services related to the hosted websites are always spread across multiple servers; the systems are ‘load balanced’ to ensure that websites are always available since load balancing makes the use of the server which is being used at the given time of the request for any service - it goes one step further from redundancy since normal redundancy just makes the use of several servers, but does not spread the information out to ensure the maximum reliability is achieved. An example of load balancing would be an end user requesting a page on a website which is hosted on a clustered hosting service; all the web servers within the cluster are too busy serving other websites, so the user is served the web page from a server which is currently free and not serving too many visitors, it also has a low CPU usage at this point because it is not being utilized much. Some web hosts allow you to purchase power for your website; what is meant by power is ‘CPU’ or ‘RAM’, this is because a clustered server pool is a more or less infinite source of resources, and is perfect if you are unable to afford a dedicated server which can match the specifications and reliability of clustered website hosting.

Security

With standard shared website hosting, the security which is provided on both the hosting node and the network is pretty poor when compared to that of a standard clustered website hosting network. In most cases, a standard shared hosting network incorporates a basic hardware firewall as the main line of security to keep a number of server secure; after that layer of security it is then down to security software installed on the servers to fight back any attack or to stop any intruder from accessing the server and compromising any information that it hosts. With a clustered hosting network, the security is normally much more stronger as a series of hardware firewalls as well as redundant proxy, routing and switching technology to ensure that the network is both fast and secure; intelligent routing can help load balance information across multiple servers, along with the use of VPNs and proxies the intelligent routing is also able to bind more than one server to just one IP address to ensure that if one server on one IP does go down, there is a number of other servers to take over its role. This type of network architecture can benefit both the servers and their users / websites that they host during a DDos attack; this is because the attack is being dispersed amongst a large pool of servers in which it is having no effect, when the attack is aimed at one piece of equipment, that piece autmatically stops serving traffic because it is unable to take the strain.

High Availability Cluster

A high availability cluster is one that makes use of several physical hosting nodes with a goal of achieving a reliable network for a certain service which it has been built to host. High availability clusters are normally deployed for things such as file sharing, business class enterprises, customer services (specifically e-commerce websites) and mission-critical databases; all these types of business related IT activities are of the utmost importance for some companies and it is important that the information for them can be accessed when needed, this is the reason for deploying a high availability cluster to host them - albeit at a high cost. The automation processes involved are fairly complicated; nodes have the ability to start services on each other if the service concerned has gone down on another node - they can also carry out the appropriate processes automatically in order to start a service if needed, such as the importing and mounting of file systems. However ‘good’ this high availability may seem, the automation processes involved in it can easily cause problems; for example if the private ‘heart beat’ connection between the nodes goes down, then each node could think that every other node is down when in fact they aren’t and lead to an instance of a service being started although that service is the responsibility of another node - this could lead to data corruption, or even worse: data loss. Implementations of high availability clusters are sometimes put in to increase the reliability of a regular cluster; via the use of things such as storage area networks (SANs) and the erradication of single points of failure; multiple network connections are also used to ensure that there is always at least one connection route available, even if one does fail. Most nodes take advantage of a number of technologies to ensure that they can provide the utmost best reliability. Hard disk wise, they take advantage of disk mirroring meaning that if one internal disk does fail, another internal disk which is a mirror of the main one can take over to ensure that the server carries on running - the technical term for this is RAID (’Redudant Arrays of Inexpensive Disks’). Redundant network connections are also utilized to ensure that if one switch or network interface card fails, there will be another one network switch or network interface card available to ensure that the node stays connected to both the network and the internet. Most of the storage on a clustered network is taken care of by networked storage devices; multiple connections to the storage area network are also used to ensure that files can always be accessed. Multiple power connections are also available for servers via the use of UPS and diesel generators which can be used in the event of a power outage of sorts. The use of multiple connections and other devices ensures that even in the event of connections going because of a fault, the cluster will still be able to operate.

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