Building a stable infrastructure for growth
Deb Shinder
Published: 09 Aug 2005 11:45 BST
As your organisation grows, so does the load on your servers. More employees means more people logging onto your domain controllers and more people accessing your file and print servers. Your expanding workforce may also include telecommuters, travelling executives, and other off-site workers, which results in more "outsiders" putting a greater load on your remote access (dialup and VPN ) servers. A growing reputation and more customers or clients mean more people simultaneously visiting your Web sites and putting a greater burden on your Web servers.
The problem is there are limits on how much of a good thing an individual server can take. If its capacity is exceeded, bad things happen: performance slows to a crawl, or worse, the server crashes from the overload and becomes unavailable to everyone.
What's the solution? You might try upgrading the server's hardware — adding more memory, adding another processor, adding more hard disk capacity — but there is a point of diminishing returns. The motherboard will generally support only a maximum amount of RAM or number of processors, and some applications aren't able to take advantage of multi-processing.
Think about what you do during a growth period in your business when the workload on one of your employees becomes too much for him or her to handle. You may try to help the employee find a way to do more, up to a point — but eventually, you have to hire another employee and divide the work between them. That's exactly what load balancing does for your overburdened servers.
How load balancing works
Load balancing involves creating a cluster of servers — a group of separate physical machines that are configured with the same applications and work like one logical server. Each of the physical servers is called a node, and a cluster can consist of two or more nodes that share the workload and provide fault tolerance because if one node fails, another takes over so that the applications or resources are still available and users typically never know a server is down.
Load balancing can be used for many types of servers/services. Web farms are groups of Web servers networked to distribute the load across the group. When many requests come in at once, some are sent to each node so that no one node is overwhelmed. Note that some server applications are not compatible with load balancing.
Load balancing requires special software that allows all the servers in the cluster to present themselves on the network as a single entity with a single (virtual) IP address. Each node also has a dedicated IP address that identifies it individually and is used to access that specific node.
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