A load balancer in information technologies and network infrastructure is a virtual device that distributes network or application traffic across a cluster of servers. This load distribution process increases the availability and reliability of applications and websites, ensuring user requests are serviced with minimal delays and are evenly distributed to prevent individual servers from being overwhelmed.

Main Features

A well-functioning load balancer should include the following key features:

  1. Traffic Distribution: A primary function of a load balancer is to distribute incoming network traffic across multiple servers to ensure no single server bears the entire load. This feature can increase the performance of applications significantly.
  2. Scalability: Load balancers allow organizations to handle increased load effortlessly by adding more servers to the infrastructure.
  3. Redundancy: If one server fails, the load balancer will redirect traffic to the remaining online servers. By doing this, it ensures high availability and reliable application performance.
  4. Session Persistence: Some applications require a user’s multiple requests to be directed to the same server each time during a single session. This feature is essential in e-commerce applications where shopping carts are used.
  5. SSL Offloading: The load balancer can manage SSL encryption/decryption, removing the resource-intensive process from web servers to improve overall performance.
  6. Health Checks: Load balancers routinely check the health of all servers in the pool to ensure they are responsive. If a server is unresponsive, the load balancer will automatically stop sending it traffic.

Load Balancer vs. Reverse Proxy

While a load balancer and a reverse proxy can perform similar roles in specific scenarios, they serve different primary functions.

As the name suggests, a reverse proxy acts as an intermediary for requests from clients seeking resources from a server. It retrieves resources on behalf of the client from one or many servers and returns them to the client as if they originated from the proxy server itself.

A load balancer, however, primarily distributes traffic among several servers to optimize resource use, maximize throughput, minimize response time, and prevent overload of any single server.

A reverse proxy can perform load-balancing functions, but its primary goal is not always to distribute load but to control and optimize resource access. On the other hand, a load balancer focuses more on optimizing resource use and ensuring high availability and reliability.

There are numerous load-balancing software solutions available. Some popular choices include:

  1. HAProxy: An open-source software offering high availability, load balancing, and proxying for TCP and HTTP-based applications. It is widely used because of its reliability, high configurability, and low memory footprint.
  2. Nginx: A powerful open-source software that can act as a web server, reverse proxy, and load balancer. It’s renowned for its performance and stability.
  3. AWS Elastic Load Balancing (ELB): A cloud-based load balancing solution by Amazon Web Services. It automatically distributes incoming application traffic across multiple targets, such as EC2 instances.
  4. Google Cloud Load Balancing: A scalable, fully distributed, software-defined managed service for all your traffic. It allows you to scale your applications on Google Cloud.
  5. F5 BIG-IP: A suite of application delivery services that provides the granular control, scalability, and security needed to ensure applications are fast, available, and secure.

Software vs. Hardware Load Balancers

Software and hardware load balancers perform the same task of distributing network traffic, but there are differences in cost, scalability, and deployment flexibility.

Hardware load balancers are dedicated physical devices, typically rack-mounted, explicitly designed for load balancing. They are equipped with specialized processors and hardware components to handle network traffic efficiently. Some notable examples include:

  1. F5 BIG-IP Local Traffic Manager (LTM): A high-performance, hardware-based load balancer from F5 Networks that offers entire proxy architecture to optimize the speed and reliability of applications.
  2. A10 Networks Thunder ADC is another series of hardware load balancers that provides advanced traffic management features. They are known for their scalability and resilience.
  3. Citrix ADC: Formerly known as NetScaler ADC, this is a hardware-based load balancer that provides high availability, load balancing, and centralized management.
  4. Radware Alteon: This load balancer delivers web performance and provides security for applications in virtual, cloud, and software-defined data centers.
  5. Barracuda Load Balancer ADC: This affordable, enterprise-grade load balancing solution delivers high availability and improved application performance.

The main differences between hardware and software load balancers can be outlined as follows:

Performance: Hardware load balancers are built with dedicated, purpose-built hardware optimized for high-speed data processing, offering excellent performance. However, advancements in software-based solutions and modern server hardware have closed the gap significantly.

Scalability: Software load balancers can be more easily scaled by simply deploying the software on additional servers. On the other hand, scaling hardware load balancers usually involves purchasing and deploying more devices, which can be costly and time-consuming.

Cost: Hardware load balancers typically have higher upfront costs than their software counterparts due to the specialized physical components involved. However, software load balancers may incur ongoing charges for licensing and support.

Flexibility: Software load balancers offer greater flexibility. They can run on various platforms, on-premises or in the cloud, and can be integrated into DevOps workflows for agile deployment and scaling. Hardware load balancers, by nature, are less flexible and are typically deployed in on-premises data centers.

Deployment & Management: Hardware load balancers require physical space in a data center and power and cooling infrastructure. They also require hardware-level maintenance and upgrades. Software load balancers, being virtual, do not have these requirements and can be managed remotely.

It’s important to note that the choice between hardware and software load balancers will depend on the specific needs and circumstances of your needs. For instance, while a software load balancer may be ideal for a cloud-based setup due to its scalability and flexibility, a hardware load balancer might be a better fit for an organization that requires high-performance load balancing in a local data center environment.