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Understanding Load Balancing: A Beginner's Guide

system design4 min read

In system design, load balancing is a crucial technique for ensuring that a system can handle a large volume of traffic or requests without being overwhelmed. In this post, we will explore what load balancing is, its benefits, limitations, and why it should be used. We will also describe different types of load balancers and common load balancing technologies.

What Is Load Balancing?

Load balancing refers to the distribution of incoming network traffic or requests across multiple servers. This is done to ensure that no single server becomes overwhelmed with traffic and fails to respond, resulting in downtime or service disruptions.

Load balancing can be achieved through various techniques such as round-robin, weighted round-robin, IP hash, and least connections. Load balancers can be hardware-based or software-based and can be placed either in front of or behind a firewall.

Benefits of Load Balancing

Load balancing has several benefits, including:

  • Improved performance and availability: Load balancing distributes traffic across multiple servers, ensuring that the system is available even if one or more servers fail.
  • Scalability: Load balancing allows for the addition of more servers to the system as demand increases.
  • Reduced response times: Load balancing ensures that requests are evenly distributed among the available servers, reducing the response time of the system.

Limitations and Challenges of Load Balancing

Despite its benefits, load balancing has some limitations and challenges, including:

  • Cost: Hardware-based load balancers can be expensive to acquire and maintain.
  • Complexity: Load balancing can be complex to set up and maintain, requiring a high level of expertise and experience.
  • Single point of failure: The load balancer itself can become a single point of failure, and its failure can result in service disruptions.

Common Load Balancing Techniques

Round Robin

This technique evenly distributes incoming traffic across all available servers in a cyclic manner. Each incoming request is sent to the next server in the list, ensuring that no server is overloaded with traffic.

Weighted Round Robin

This technique is similar to round-robin, but it allows administrators to assign weights to each server based on its processing power or available resources. Servers with higher weights receive a larger share of the incoming traffic.

Least Connections

This technique directs incoming traffic to the server with the least number of active connections. This ensures that traffic is distributed evenly across servers, regardless of their processing power or available resources.

IP Hashing

This technique uses the source IP address of incoming traffic to determine which server to route the traffic to. Each unique IP address is mapped to a specific server, ensuring that traffic from the same IP address is always directed to the same server.


This technique examines the content of incoming traffic to determine which server to route the traffic to. For example, traffic containing images or videos might be directed to a server with more storage capacity, while traffic containing database queries might be directed to a server with more processing power.

Types of Load Balancers

  • Network Load Balancer: These load balancers operate at the transport layer (Layer 4) of the OSI model and can only route traffic based on IP address and port.
  • Application Load Balancer: These load balancers operate at the application layer (Layer 7) of the OSI model and can route traffic based on the content of the request.
  • Global Load Balancer: These load balancers can distribute traffic across multiple data centers and regions, ensuring high availability and reducing latency.

Common Load Balancing Technologies

  • Nginx: Nginx is a software-based load balancer that is highly scalable and widely used.
  • HAProxy: HAProxy is a software-based load balancer that supports multiple protocols and is highly available.
  • Amazon ELB: Amazon ELB is a cloud-based load balancer that is fully managed and highly available.

Final Thoughts

Load balancing is a crucial technique in system design that helps to improve performance, availability, and scalability while reducing response times. Different types of load balancers and technologies can be used based on the specific requirements of the system. It is important to carefully consider the benefits and limitations of load balancing before implementing it.

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