Skip to main content

Load balancing

 

Load balancing is a technique used to distribute workloads uniformly across servers or other compute resources to optimize network efficiency, reliability and capacity. Load balancing is performed by an appliance -- either physical or virtual -- that identifies in real time which server in a pool can best meet a given client request, while ensuring heavy network traffic doesn't unduly overwhelm a single server.

In addition to maximizing network capacity and performance, load balancing provides failover. If one server fails, a load balancer immediately redirects its workloads to a backup server, thus mitigating the impact on end users.

Load balancing is usually categorized as supporting either Layer 4 or Layer 7. Layer 4 load balancers distribute traffic based on transport data, such as IP addresses and Transmission Control Protocol (TCP) port numbers. Layer 7 load-balancing devices make routing decisions based on application-level characteristics that include HTTP header information and the actual contents of the message, such as URLs and cookies. Layer 7 load balancers are more common, but Layer 4 load balancers remain popular, particularly in edge deployments.

How load balancing works

Load balancers handle incoming requests from users for information and other services. They sit between the servers that handle those requests and the internet. Once a request is received, the load balancer first determines which server in a pool is available and online and then routes the request to that server. During times of heavy loads, a load balancer can dynamically add servers in response to spikes in traffic. Conversely, they can drop servers if demand is low.

A load balancer can be a physical appliance, a software instance or a combination of both. Traditionally, vendors have loaded proprietary software onto dedicated hardware and sold them to users as stand-alone appliances -- usually in pairs, to provide failover if one goes down. Growing networks require purchasing additional and/or bigger appliances.

In contrast, software load balancing runs on virtual machines (VMs) or white box servers, most likely as a function of an application delivery controller (ADC). ADCs typically offer additional features, like caching, compression, traffic shaping, etc. Popular in cloud environments, virtual load balancing can offer a high degree of flexibility -- for example, enabling users to automatically scale up or down to mirror traffic spikes or decreased network activity.

Load-balancing methods

Load-balancing algorithms determine which servers receive specific incoming client requests. Standard methods are as follows:

  • The hash-based approach calculates a given client's preferred server based on designated keys, such as HTTP headers or IP address information. This method supports session persistence, or stickiness, which benefits applications that rely on user-specific stored state information, such as checkout carts on e-commerce sites.
  • The least-connections method favors servers with the fewest ongoing transactions, i.e., the "least busy."
  • The least-time algorithm considers both server response times and active connections -- sending new requests to the fastest servers with the fewest open requests.
  • The round robin method -- historically, the load-balancing default -- simply cycles through a list of available servers in sequential order.

Formulas can vary significantly in sophistication and complexity. Weighted load-balancing algorithms, for example, also take into account server hierarchies -- with preferred, high-capacity servers receiving more traffic than those assigned lower weights.


Comments

Post a Comment

Popular posts from this blog

Ghosting

Ghosting is to cease communications without notification. The use of the word "ghost" as a verb originated in social media in reference to dating, but the term is now used by employers to describe employees and potential employees who suddenly disappear. Typically, ghosting is used to describe: Job candidates who suddenly stop responding to messages. New hires who fail to show up for their first day of work. Employees who do not show up for a shift. Employees who leave work in the middle of the day and never come back. Some analysts blame ghosting on millennial entitlement. The reasoning is that members of the millennial generation have been brought up to feel they are special -- so special, in fact, that they do not need to follow conventional rules of behavior. Other analysts, however, maintain that ghosting behavior stems from changes in the job market and the phenomenon is simply a reflection of the laws of supply and demand in a healthy jo...
Post a Comment
Read more

Data deduplication

Data deduplication -- often called intelligent compression or single-instance storage -- is a process that eliminates redundant copies of data and reduces storage overhead. Data deduplication techniques ensure that only one unique instance of data is retained on storage media, such as disk, flash or tape. Redundant data blocks are replaced with a pointer to the unique data copy. In that way, data deduplication closely aligns with incremental backup, which copies only the data that has changed since the previous backup. For example, a typical email system might contain 100 instances of the same 1 megabyte (MB) file attachment. If the email platform is backed up or archived, all 100 instances are saved, requiring 100 MB of storage space. With data deduplication, only one instance of the attachment is stored; each subsequent instance is referenced back to the one saved copy. In this example, a 100 MB storage demand drops to 1 MB. Target vs. source deduplication Data deduplica...
Post a Comment
Read more

A Graphics Processing Unit (GPU)

A graphics processing unit (GPU) is a computer chip that performs rapid mathematical calculations, primarily for the purpose of rendering images. A GPU may be found integrated with a central processing unit (CPU) on the same circuit, on a graphics card or in the motherboard of a personal computer or server. In the early days of computing, the CPU performed these calculations. As more graphics-intensive applications such as AutoCAD were developed; however, their demands put strain on the CPU and degraded performance. GPUs came about as a way to offload those tasks from CPUs, freeing up their processing power. NVIDIA, AMD, Intel and ARM are some of the major players in the GPU market. GPU vs. CPU A graphics processing unit is able to render images more quickly than a central processing unit because of its parallel processing architecture, which allows it to perform multiple calculations at the same time. A single CPU does not have this capability, although multi...
Post a Comment
Read more