Master Nginx Load Balancing: Round‑Robin, Weighted, IP‑Hash & Least‑Conn Explained

Nginx is a high‑performance HTTP and reverse‑proxy server that can also act as a load balancer.

It can distribute traffic among multiple backend servers, improving availability, scalability, and performance.

Load‑balancing algorithms

The common algorithms include round‑robin, weighted, IP‑hash, and least‑connections, each suited to different scenarios.

1. Round‑robin

The default strategy assigns requests to servers in a fixed order, ideal when backend servers have similar capacity.

Configuration example:

http {
    upstream mikechen {
        server backend1.mikechen.cc;
        server backend2.mikechen.cc;
        server backend3.mikechen.cc;
    }

    server {
        listen 80;

        location / {
            proxy_pass http://mikechen;
        }
    }
}

2. Weighted

Weighted load balancing lets you assign different weights to servers so that more powerful servers receive more requests.

Example weights:

server backend1.mikechen.cc weight=5;
server backend2.mikechen.cc weight=3;
server backend3.mikechen.cc weight=1;

3. IP‑hash

IP‑hash hashes the client’s IP address to consistently route a user to the same backend, useful for session‑affinity.

http {
    upstream backend {
        ip_hash;
        server backend1.example.com;
        server backend2.example.com;
        server backend3.example.com;
    }

    server {
        listen 80;
        server_name example.com;

        location / {
            proxy_pass http://backend;
            proxy_set_header Host $host;
            proxy_set_header X-Real-IP $remote_addr;
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
            proxy_set_header X-Forwarded-Proto $scheme;
        }
    }
}

4. Least‑connections

The least‑connections method sends new requests to the server with the fewest active connections, helping balance uneven request processing times.

http {
    upstream backend {
        least_conn;
        server backend1.example.com;
        server backend2.example.com;
        server backend3.example.com;
    }

    server {
        listen 80;
        server_name example.com;

        location / {
            proxy_pass http://backend;
            proxy_set_header Host $host;
            proxy_set_header X-Real-IP $remote_addr;
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
            proxy_set_header X-Forwarded-Proto $scheme;
        }
    }
}

These configurations enable efficient traffic distribution and can be chosen based on server capacity, session requirements, or request latency characteristics.