What Is a Load Balancer? Explained Simply

What a load balancer is

A load balancer is a system that sits in front of a group of servers and distributes incoming network requests across them. Instead of every visitor hitting one server, the load balancer spreads the traffic so each server handles a share of the work. It acts as a single entry point for users while quietly directing their requests to whichever backend server is best positioned to respond, which keeps a busy service fast and available.

Why it is needed

A single server has limits. As traffic grows, one machine can become overwhelmed, slowing down or crashing. Running multiple servers solves the capacity problem, but then you need a way to share work among them, that is the load balancer's job. It also improves reliability: if one server fails, the balancer can route around it to the healthy ones, so the service keeps running. This combination of scalability and resilience is why essentially every large website uses load balancing.

How it distributes traffic

Load balancers use algorithms to decide where each request goes. 'Round robin' simply rotates through the servers in order. 'Least connections' sends new requests to the server currently handling the fewest. Others factor in response times or server capacity. Some setups also use 'sticky sessions' to keep a given user on the same server when that matters. The right method depends on the application, but the goal is always the same: keep any single server from becoming a bottleneck.

Health checks

A key feature of load balancers is health checking. The balancer regularly tests each backend server to confirm it is responding correctly. If a server fails these checks, perhaps it crashed or is overloaded, the balancer stops sending it traffic and redirects requests to the healthy servers. When the server recovers, it is added back into rotation. This automatic failover is a big part of how large services stay online even when individual machines have problems.

Where load balancers live

Load balancing can happen at different levels. Hardware load balancers are dedicated appliances; software load balancers run on ordinary servers; and cloud providers offer managed load balancing as a service you can turn on with a few clicks. Balancers also operate at different network layers, some make decisions based on basic network information, others look at the actual web request to route more intelligently. The concept is the same regardless of where it runs.

Why it matters

Load balancing is one of the core techniques that lets web services handle massive scale without falling over. Understanding it explains how a site can serve millions of users at once, survive the failure of individual servers, and be updated without downtime. It is a foundational building block of reliable, high-traffic infrastructure, and a concept that appears constantly once you start looking at how modern applications are deployed.

Related on Skillo

See also: What is a server? Explained simply, What is a microservice architecture?.

Sources

• Load balancing (computing) - Wikipedia

Published date reflects the original event date (2025-02-18). This article is original Skillo editorial written from the sources above; facts were verified in September 2026.