Traditionally, server load balancing has been viewed as a problem for large enterprises and a costly and unnecessary expense for SMEs. But, that was when most SMEs ran their businesses using just a couple of servers. Today, the number of servers used by SMEs can be as many as 10 or more, making server load balancing a must-have item on the IT shopping list.
Furthermore, with back-end applications such as order processing, billing and customer management being integrated into complete supply-chain, Web-enabled applications, Web site reliability, scalability and performance is essential. To deal with this, a new breed of server load balancers has evolved, called application delivery controllers - or ADCs - that provide the ability to direct Internet Web traffic to the best performing, most accessible servers based on factors such as concurrent connections and CPU/memory utilisation. If a server or application fails, the user is automatically rerouted to another functioning server.
ADCs use various techniques to distribute traffic load between two or more servers, routers, firewalls, and other networked resources, to optimise utilisation and improve performance and response time. Most ADCs are capable of providing Layer 4 to Layer 7 management. Layer 4 is limited to Web requests destined to TCP Port 80; therefore, no further differentiation among server groups is possible. Layer 7 switching uses application-layer criteria to determine where to send a request to provide more granular control over forwarding decisions.
Content switching is used to distribute or balance user requests to servers based on Layer 7 payload. Most commonly, this is done by examining page content such as a URL and 'switching' requests to the appropriate server or group of servers. For example, www.xyz.com/images may be pointed to a server that handles graphics, while the www.xyz/shop may be pointed to a transaction server. In addition, if a Web application makes extensive use of cookies, a Layer 7-capable ADC can switch users based on cookie values, providing a much better model for achieving server persistence.
To further enhance and secure the user experience, more-advanced ADCs also provide SSL offload/acceleration that enables processor-intensive SSL handshake and encryption/decryption processes to be removed from the servers. This offloading dramatically increases server performance, while decreasing the time and costs associated with SSL certificate management.
In addition, Layer 7 capable ADCs provide for application-level health checking and provide a more accurate means of establishing server persistence.
Another big driver for server load balancing among SMEs is the list of changes Microsoft has made to its core server architecture in Exchange 2010. Now that Exchange Client Access Server (CAS) is used to handle all client connections, it is important to ensure that e-mail users do not suffer from poor performance and user experience by providing load balancing to automatically reroute and reconnect e-mail users to functioning servers.
As well as the migration to Exchange 2010, many SMEs adopting Microsoft SharePoint and Lync Server technologies are discovering the need for load balancing. In fact, Microsoft increasingly recommends the use of server load balancing to optimise performance and resilience.
While large enterprise load balancing solutions have been too costly and complex for SMEs, there is a new generation of affordable hardware or virtual load balancers or ADCs designed for SMEs. The complexity and scale of technology required to run today's SMEs has brought with it many new challenges to deliver performance, high availability and security. SME IT is the same as enterprise IT in everything but scale, and if SMEs want the functionality and quality that enterprise CIOs take for granted, load balancing has to be part of the equation.
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