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Jun 26 2015

Load Balancing Special, Pt. 1: What Are Load Balancers and How Do They Work?


Modern web and application infrastructures are continuously expanding: shop systems, customer communication, order management, helpdesks, internal collaboration and communications as well as various backend applications all demand their fair share of server performance and uptime. To prevent this slew of systems from cannibalizing each other, large corporations have long used efficient network management techniques and a special type of network device called a server load balancer or application delivery controller. Our four-part blog provides you with a first insight into the technology and how it can be put to good use in SMB scenarios.

In today's hyper-connected economy, every organization has to be permanently available. Until a few years back, this rule only applied to the so-called big players, regardless of which industry they belonged to or which time zone they were located in. But nowadays, even the small bicycle store across the street is likely to run a web shop and an app – and have a bunch of clients who use them. The web shop and app will in turn require functional customer and spare parts databases to feed off. As it continues to expand, the bicycle store will sooner or later encounter the same problems as the 'big guys' did. And likewise, it'll have to deploy the same key technologiesto fend them off.

Among the most important of these key technologies are server load balancers and their more advanced cousins, called application delivery controllers (ADCs). In essence, both device types serve the same purpose: distributing workloads across multiple servers in order to optimize throughput, response times, and hardware utilization and avert the proverbial curses of modern IT infrastructures, sluggish performance and downtimes. On a more abstract level, they help to improve application and web service performance, reliability/stability, and scalability and simplify server management – all of which translates into competitive advantages over the medium term.

Popular and Detailed Definitions
So what exactly are server load balancers and ADCs? Explained in simple terms, a load balancer is a server that directs network traffic, such as incoming requests or orders, to the adequate backend systems, which in turn respond by sending a reply to the load balancer, which then forwards it to the party that sent the request or order (see the diagram below). In other words, a load balancer is something like a "network traffic cop." An ADC is basically an advanced type of server load balancer with a broader feature set. In both cases, the general idea is to prevent a situation where either the backend servers or the Internet connection turn into a bottleneck and massively slow down services or bring them to a complete halt.

Fig. 1: Load Balancer Diagram


Fig. 1: Load balancers and ADCs direct incoming requests to the appropriate backend systems.

A more concise definition comes from KEMP Technologies, a New York-based provider of load balancing solutions and Fujitsu Alliance Partner since 2014. According to KEMP, "[a]pplication delivery solutions were built to address the challenges associated with website infrastructure complexity, performance, scalability and security" and can be "quite diverse" in functionality, as is obvious from their multitude of names ranging from ADC through "content switch" to "web front-end." Historically, these solutions evolved from the earliest-generation server load balancers (SLBs) which first became popular in the 1990s due to the worldwide explosion of Internet traffic. Further according to KEMP, large organizations typically use one of two types of load balancers today:

  • Network server load balancers optimize the performance of servers delivering important content to in-house users, co-workers from other companies or the general public.
  • Line load balancers aggregate XDSL WAN connections.

Load balancers are either available as hardware appliances or as virtual load balancers, i.e. a special type of software loaded on an optimized platform. Both types perform two critical key tasks:

  • Based on the chosen method of distributing network/Internet traffic, they deliver requests to the best network servers as fast and efficiently as possible.
  • While in action, they continually check the performance of the network servers and make decisions which server is performing in the best way to serve user demands.

These are also the core capabilities of a standard ADC. In addition, ADCs can transparently take servers or applications offline if a failure occurs and redirect incoming requests to a functional machine. More advanced models also offer features such as SSL acceleration, content caching, and data compression while enabling administrators to use more granular network management strategies to 'redirect' network traffic internally.

We'll discuss these key features as well as some typical use cases in part 2 of this blog.

Thomas Kurz


About the Author:

Thomas Kurz

Guest author, Director Channel & Alliances DACH, EE & MENA KEMP Technologies Europe.


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