Server load balancing is an advanced technique (using load balancing hardware or programs) designed to distribute the work load to optimize IP-based queries from the Internet or Intranet throughout a server farm.
The method most commonly used is server clusters, especially high availability clusters.
After the initial set-up, the administrator adapts these methods or scheduling rules to your specific requirements. To simplify, server load balancing is like taking several individual servers and making them appear as one giant server. This is called clustering. In the most extreme cases, you can even have several clusters of servers and load balance across these separate clusters. You might see this on a high-demand site like YouTube.
There are many reasons a company benefits by upgrading to a load-balanced solution, but the most common are scalability, high availability, and predictability. Consider a company with a website that is accessed thousands of times a day, hosted on a dedicated server. Regardless of their company's size, IT managers need to be confident:
Scalability lets you handle sudden and/or gradual increases in traffic. Ideally, as you grow your web presence, you will have more people visiting your site, viewing more pages, and making more requests. If you have a single server, these increases can overwhelm your server and result in downtime. If you need to upgrade, you will experience similar downtime as you move to the new server. Server load balancing allows you to seamlessly scale your hardware as needed.
Imagine you have a farm, and each year you plow a bigger field—or one year start a second field. If you have a one-horse plow, you might plan to buy a younger, stronger horse or get a new plow, but you'd need to take time away from farming to go find and buy your selections. Instead, you could simply add a second horse to the team to balance the extra work needed. Eventually, you may need to have two teams of two-horse plows, but you can easily plan to scale up to that.
The farm is like your web traffic, and the horses are like your servers. By adding a second server, you can balance the workload across both servers, and if needed, you can add an entire additional cluster of servers - planning to scale up all the way.
High availability meas your site is available all the time, 24x7x365. With only a single server, the site will need to be taken down when you perform maintenance or upgrade your hard drive or RAM. During that downtime, customers might find their way to your competition. With server load balancing, you can upgrade or run maintenance on one server, and the additional requests are automatically sent to the rest of the servers in the cluster.
Using our farm analogy, if you have a one-horse team, your horse may get sick or need to be re-shoed, meaning you can't plow your field. If you have a multi-horse team, the rest of the horses can work a bit harder to complete the plowing without anyone really noticing the difference.
Predictability provides users a consistent experience each time they visit. You may have certain times of day that more people visit your site, or you may run a promotion or release a new service. This is similar to the Slashdot effect. With a single server, peak times may mean a painfully slow website or web application. Customers may get frustrated and leave. With multiple servers, these peaks are easily addressed by sharing the workload. Comparing this to our farm, in the summer, your trusty horse may slow down or may not be able to work at all in the afternoon sun. With several horses working together, working in the heat isn't as big an issue because the workload is being shared.
Adding a more efficient server or improved network hardware alone will not meet all of your requirements, since it can improve only on the performance - this is like simply replacing your horse or your plow. To attain a high level of availability with minimum downtime and fast access speeds, we recommend that you have two or more dedicated servers operating simultaneously. These mirrored servers must then be load balanced for automatic failover and detection of poor application performance in any of the online servers. If one mirror server fails, another mirror server takes over automatically. The server load balancer knows the extent of the load on the servers, so it can direct queries in the most efficient and best possible way.
There are a few methods for server load balancing and they are listed below.
NOTE: The best method for your business depends on your application and the types of servers that you have running.
