How to Configure a Load Balancer on Nginx -

Here’s a step-by-step guide for setting up a load balancer on Nginx to efficiently distribute traffic across multiple backend servers.

This setup is commonly used to improve application performance, ensure availability, and support redundancy.

I will use an Ubuntu server for this article.

Step 1: Install Nginx #

If you haven’t installed Nginx, start by installing it on the server you’ll use as your load balancer.

Update the System Packages #

sudo apt update

Install Nginx #

On Debian-based systems like Ubuntu, you can install Nginx with:

sudo apt install -y nginx

On RHEL-based systems, like Almalinux, CentOs use:

sudo dnf install -y nginx

After installation, start and enable Nginx:

sudo systemctl start nginx
sudo systemctl enable nginx

Step 2: Configure the Load Balancer #

Open the Nginx Configuration File #

Edit the Nginx configuration file to define the load balancer settings.

Use either the default configuration file at /etc/nginx/nginx.conf or create a new one in the /etc/nginx/conf.d/ directory.

sudo nano /etc/nginx/conf.d/load_balancer.conf

Define the Upstream Servers #

In the configuration file, define the backend servers (also called “upstream servers”) that will handle the load. Add the following section, replacing the IP addresses with those of your backend servers:

upstream backend_servers {
server 192.168.1.10; # Server 1
server 192.168.1.11; # Server 2
server 192.168.1.12; # Server 3
}

Set Up the Load Balancing Configuration #

Now configure a server block to route incoming requests to the defined upstream servers:

server {
    listen 80;

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

This configuration instructs Nginx to listen on port 80 and forward all traffic to the servers defined in the upstream backend_servers block.

Step 3: Load Balancing Algorithms #

Nginx offers several load balancing algorithms. The default algorithm is Round Robin, but you can also configure it for Least Connections or IP Hash.

Round Robin (default) – Distributes traffic equally among all servers:

upstream backend_servers {
server 192.168.1.10;
server 192.168.1.11;
}

2. Least Connections – Directs traffic to the server with the fewest active connections, which helps balance load dynamically:

upstream backend_servers {
least_conn;
server 192.168.1.10;
server 192.168.1.11;
}

3. IP Hash – Sends requests from the same client IP to the same backend server, which can be useful for session persistence:

upstream backend_servers {
ip_hash;
server 192.168.1.10;
server 192.168.1.11;
}

Choose the algorithm that best suits your needs and adjust the upstream block accordingly.

Step 4: Enable Health Checks (Optional) #

Nginx doesn’t natively support active health checks in the free version, but you can set a passive health check by configuring proxy_next_upstream directives to route requests away from failed servers.

upstream backend_servers {
    server 192.168.1.10;
    server 192.168.1.11;
    server 192.168.1.12;
}

server {
    listen 80;

    location / {
        proxy_pass http://backend_servers;
        proxy_next_upstream error timeout invalid_header http_500 http_502 http_503 http_504;
        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;
    }
}

In this configuration, Nginx will skip to the next server if it encounters errors like a timeout or a 500-series HTTP error.

Step 5: Apply and Test the Configuration #

Check Nginx Syntax #

Run the following command to check the syntax of your Nginx configuration:

sudo nginx -t

If the syntax is correct, restart Nginx to apply the changes:

sudo systemctl restart nginx

Verify the Load Balancer #

Access the IP address or domain of your Nginx server (the load balancer) from a web browser to confirm that traffic is correctly routed to the backend servers. You can also use tools like curl or ab (Apache Bench) to send multiple requests and confirm that they are distributed across servers.

curl http://your_load_balancer_ip

Step 6: Additional Configuration (Optional) #

You can further customize the load balancer by:

Configuring SSL for secure connections
Setting a custom error page for when all backend servers are down
Adding rate limiting to protect your backend servers

Author’s Final Word #

This configuration gives you a robust Nginx load balancer setup to handle incoming requests and distribute them across multiple backend servers, improving your application’s scalability and reliability