What is Load Balancing? How Load Balancing Works | TechTarget

What is load balancing?

Load balancing is a technique used to distribute network traffic across a pool of servers known as a server farm. It optimizes network performance, reliability and capacity, reducing latency as the demand is equally distributed among multiple servers and compute resources.

Load balancing uses an appliance — either physical or virtual – to identify in real time which server in a pool can best meet a given client request, while ensuring heavy network traffic doesn’t unduly overwhelm a single server.

In addition to maximizing network capacity and ensuring high performance, load balancing provides failover. If one server fails, a load balancer immediately redirects its workloads to a backup server, thus mitigating the effect on end users.

Load balancing is usually categorized as supporting either Layer 4 or Layer 7 of the Open Systems Interconnection (OSI) communication model. Layer 4 load balancers distribute traffic based on transport data, such as IP addresses and TCP port numbers. Layer 7 load-balancing devices make routing decisions based on application-level characteristics, which include Hypertext Transfer Protocol (HTTP) header information and the actual contents of the message, such as URLs and cookies. Layer 7 load balancers are more common, but Layer 4 load balancers remain popular, particularly in edge deployments.