Load Balancers Explained

Imagine launching an application that suddenly receives one million requests per day. If every request is handled by a single server, that server eventually becomes overloaded, causing slow responses or complete downtime.

A Load Balancer sits in front of multiple servers and intelligently distributes incoming traffic across them. This improves performance, increases availability, and removes the single point of failure from the architecture.

A single backend server has finite CPU, memory, network bandwidth, and storage. As traffic increases, response times become slower until the server can no longer handle incoming requests.

Instead of continuously upgrading a single machine (vertical scaling), organizations deploy multiple application servers behind a load balancer to distribute traffic efficiently.

Clients never communicate directly with backend servers. Every request first reaches the load balancer.

The load balancer determines which healthy server should receive the request using a routing algorithm such as Round Robin or Least Connections.

The difference between these two architectures becomes significant as application traffic grows.

Different algorithms are appropriate for different workloads and infrastructure.

A load balancer continuously checks whether backend servers are healthy.

If one server becomes unavailable, the load balancer automatically removes it from the routing pool until it recovers.

Popular load balancing solutions include NGINX, HAProxy, AWS Application Load Balancer (ALB), AWS Network Load Balancer (NLB), Google Cloud Load Balancer, and Azure Load Balancer.

In Kubernetes, Services and Ingress Controllers commonly provide load balancing capabilities for applications running inside the cluster.

What problem does a load balancer solve?

What is the difference between Round Robin and Least Connections?

How do health checks improve availability?

Can a load balancer become a single point of failure?

What is the difference between Layer 4 and Layer 7 load balancing?

Load balancers are fundamental building blocks of scalable distributed systems. They distribute traffic, eliminate single points of failure, improve fault tolerance, and enable applications to scale horizontally.

Whether deploying applications on cloud platforms, Kubernetes, or traditional infrastructure, understanding load balancers is an essential skill for every backend engineer.