What is a Load Balancer?

When a business assigns multiple resources to process requests for a website or application, a load balancer is deployed to manage the distribution of these requests. The primary goal of a load balancer is to balance the request load, ensuring that no single server becomes too burdened. An overloaded server may cause delays, timeouts and the mishandling or loss of requests, all of which can harm the customer experience.

How Does a Load Balancer Function?

A load balancer operates as a reverse proxy, presenting a virtual IP address (VIP) that represents the application to clients. When a client connects to the VIP, the load balancer uses its algorithms to select the most suitable server instance to handle the request. It continues to monitor the connection throughout its duration to ensure optimal performance.

In addition to routing traffic, the load balancer also manages security by filtering access and authenticating client identities. It can also perform Global Server Load Balancing, (GSLB) by redirecting requests to servers in different locations based on availability or geographic location of the client.

Benefits of Load Balancer

Customers rely on immediate access to information and efficient transaction processing. Delays or inconsistent responses, particularly during peak times, may result in permanent customer loss. Moreover, extreme spikes in computing demands can disrupt an internal server or server system when the incoming load exceeds its capacity to handle it effectively. Here are the benefits Load Balancer offers under the following parameters.

1. Availability

Load balancers enhance application availability by distributing traffic across multiple servers, preventing any single server from becoming a failure point. They continuously monitor server health to reroute traffic away from underperforming servers, reducing downtime and improving user experience. This ensures that applications remain accessible and responsive, especially during peak usage times, thereby preventing customer loss to competitors due to technical issues.

2. Scalability

Handling high-demand events requires the ability to scale resources efficiently. When thousands of users access an application simultaneously, distributing traffic across multiple servers allows for seamless performance and uninterrupted service. Load balancers dynamically allocate resources to handle surges in demand, helping businesses maintain a smooth user experience and maximize opportunities during peak traffic periods.

3. Security

Strengthening application security requires a proactive approach to traffic management. By distributing requests across multiple backend systems, load balancers reduce the attack surface, making it harder for threats to exploit vulnerabilities or exhaust system resources. If a server becomes compromised, traffic is efficiently redirected to secure alternatives, preventing disruptions. Load balancers also add a layer of defense against DDoS attacks by intelligently rerouting traffic, keeping applications protected and operational.

4. Performance

Addressing the above factors, a load balancer significantly improves application performance. It increases security, ensures consistent uptime, and scales effectively during demand spikes, keeping applications responsive and delivering a smooth experience both businesses and customers.

Types of Load Balancers

Explore the different load balancer types, each designed to manage traffic efficiently and enhance application performance across various environments.

1. Network Load Balancer

Network load balancing is the process of distributing traffic at the transport level based on network variables such as IP addresses and destination ports. Operating at the TCP/UDP level, this method does not inspect application-level details, including content types, cookie data, headers or application behavior. Instead, it relies on network address translations and connection tracking to efficiently route traffic based on network-layer information. Network Load Balancers are designed for high-performance, low-latency traffic distribution, making them ideal for handling large volumes of requests with minimal processing overhead. 

2. Application Load Balancer

An Application Load Balancer ranks at the top of OSI model. As a Layer 7 load balancer, it intelligently distribute requests using numerous application-level parameters. They evaluate a wide spectrum of data, including HTTP headers, SSL sessions, request content and cookies, making traffic allocation decisions based on multiple factors. This capability allows application load balancers to effectively control traffic optimizing user experience by directing requests according to behavior, usage patterns, and content type.

3. Global Server Load Balancer

Global Server Load Balancer (GSLB) represents a different approach compared to traditional layer 4-7 load balancers. It operates at the DNS level, acting as a DNS resolver or proxy to direct requests based on real-time load balancing algorithms. It functions as a dynamic DNS technology that manages and monitors various geographically distributed sites through configurations health checks and network conditions. Many contemporary load balancing solutions now integrate GSLB to optimize global traffic distribution and enhance redundancy across data centres.

Common Load Balancer Algorithms

The effectiveness of a load balancing solution depends on the algorithm used to route incoming requests. Different algorithms determine how packets and service requests are allocated across available servers, each offering unique advantages based on system needs. Here are some commonly used load balancing algorithms:

Round-Robin Algorithm

Network load balancing is the process of distributing traffic at the transport level based on network variables such as IP addresses and destination ports. Operating at the TCP/UDP level, this method does not inspect application-level details, including content types, cookie data, headers or application behavior. Instead, it relies on network address translations and connection tracking to efficiently route traffic based on network-layer information. Network Load Balancers are designed for high-performance, low-latency traffic distribution, making them ideal for handling large volumes of requests with minimal processing overhead. 

Weighted Round-Robin Algorithm

An enhancement of the round-robin method, this algorithm assigns a weight to each server based on its processing power and capacity. Servers with higher capabilities receive more requests than lower-capacity ones, ensuring a more balanced distribution of workloads. This approach is particularly useful in environments where servers have varying performance levels.

Least Connections Algorithm

This algorithm directs new requests to the server with the fewest active connections, under the assumption that it has more available resources. While it helps prevent server overload, it assumes that all connections require equal computing power, which may not always be the case.

Lowest Response Time Routing

A load balancing approach that directs traffic to the server with the fastest response time, minimizing latency and improving performance. Response time is measured using Time to First Byte (TTFB), where the load balancer pings servers and assigns requests to the one that replies the quickest. Ideal for latency-sensitive applications, this method enhances user experience and optimizes system efficiency.