What is load balancing, and what are common load balancing algorithms?

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Load balancing distributes incoming network traffic across multiple servers to ensure no single server becomes overwhelmed. It improves reliability, availability, and response times by spreading the workload evenly.

A load balancer sits between clients and servers, receiving all incoming requests and forwarding them to available backend servers based on certain algorithms.

Common load balancing algorithms include several approaches.

Round robin is the simplest method. Requests are distributed sequentially to each server in turn. Server one gets the first request, server two gets the second, and so on. When all servers have received a request, it starts over. This works well when servers have similar capacity.

Weighted round robin assigns weights to servers based on their capacity. A server with weight two receives twice as many requests as a server with weight one. This is useful when servers have different hardware specifications.

Least connections sends new requests to the server with the fewest active connections. This accounts for requests that take different amounts of time to process. It prevents overloading servers handling slow requests.

IP hash uses the client's IP address to determine which server receives the request. The same client always reaches the same server, which is useful for session persistence without shared session storage.

Least response time combines the least connections approach with actual response times. Requests go to the server that can respond fastest based on current conditions.

Load balancers also perform health checks, periodically testing backend servers to ensure they are responsive. If a server fails the health check, the load balancer stops sending traffic to it until it recovers.

Popular load balancer options include hardware appliances like F5, software solutions like Nginx and HAProxy, and cloud services like AWS Elastic Load Balancer or Google Cloud Load Balancing.