How does a load balancer distribute traffic between multiple servers?

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How does a load balancer distribute traffic between multiple servers?

Asked on Dec 05, 2025

Answer

A load balancer distributes incoming network traffic across multiple servers to ensure no single server becomes overwhelmed, optimizing resource use, maximizing throughput, minimizing response time, and avoiding overload. Load balancers can operate at various layers of the OSI model, such as Layer 4 (transport) and Layer 7 (application), and use algorithms like round-robin, least connections, or IP hash to determine traffic distribution.

Example Concept: A load balancer receives client requests and forwards them to one of several backend servers based on a chosen algorithm. For instance, in a round-robin setup, the load balancer forwards each new request to the next server in line, cycling through the list of servers. This helps distribute the load evenly. Advanced load balancers can also perform health checks to ensure traffic is only sent to servers that are up and running, and they can provide SSL termination and session persistence features.

Additional Comment:

Load balancers can be hardware-based (e.g., F5, Citrix ADC) or software-based (e.g., HAProxy, NGINX, AWS Elastic Load Balancing).
Layer 4 load balancers make decisions based on data from network and transport layer protocols, such as IP address and TCP/UDP ports.
Layer 7 load balancers make decisions based on application-layer data, such as HTTP headers and cookies.
Health checks are crucial to ensure traffic is directed only to healthy servers.
Load balancing improves fault tolerance and scalability of applications.

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