How to configure an nginx web server to work as load balancer

To configure Nginx as a load balancer, you need to set up multiple backend servers and define the load balancing algorithm.

Install Nginx:

Begin by installing Nginx on your server. The installation process depends on the operating system you're using. For example, on Ubuntu, you can run the following command:

sudo apt-get update
sudo apt-get install nginx

Configure Backend Servers:
Define the backend servers that will receive the incoming traffic. These servers can be separate physical machines or virtual machines. Modify the Nginx configuration file (nginx.conf) or create a new configuration file in the /etc/nginx/conf.d/ directory.

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

Replace backend1.example.com, backend2.example.com, etc., with the actual IP addresses or domain names of your backend servers. You can have as many backend servers as needed.

Configure Load Balancing:

Add the load balancing configuration within the Nginx server block. Specify the proxy_pass directive to forward the incoming requests to the backend servers defined in the previous step. Choose the appropriate load balancing algorithm based on your requirements.

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;
    }
}

In this example, the proxy_pass directive is set to http://backend, which references the previously defined upstream group named backend. The proxy_set_header directives are used to preserve the original client request headers when forwarding the request.

Round Robin Load Balancing:

http {
    upstream backend {
        server backend1.example.com weight=3;
        server backend2.example.com;
        server backend3.example.com max_fails=2 fail_timeout=30s;
    }
    
    server {
        listen 80;
        
        location / {
            proxy_pass http://backend;
            proxy_next_upstream error timeout invalid_header http_500 http_502 http_503 http_504;
        }
    }
    
    # Additional configuration...
}

In this example, we have three backend servers: backend1.example.com, backend2.example.com, and backend3.example.com. The first server has a weight of 3, meaning it will receive three times more requests compared to the other servers. The third server has additional parameters max_fails and fail_timeout, which specify the maximum number of failed attempts before considering the server as unavailable and the timeout period before considering it as active again. The proxy_next_upstream directive is added to handle certain errors and instruct Nginx to try the next server in the upstream group.

Load Balancing with IP Hash:

http {
    upstream backend {
        ip_hash;
        server backend1.example.com;
        server backend2.example.com;
        server backend3.example.com;
    }
    
    server {
        listen 80;
        
        location / {
            proxy_pass http://backend;
        }
    }
    
    # Additional configuration...
}

The proxy_pass directive is used to forward requests to the defined upstream group (backend). The ip_hash directive ensures that the same client IP address is consistently routed to the same backend server.

Fine-tuning IP hashing load balancing may involve modifying additional parameters according to your specific requirements. Some commonly used parameters include:

ip_hash with the consistent parameter: This provides a more balanced distribution of requests by reducing the potential for uneven distribution caused by varying IP address hash values.

server parameters: You can assign weights to individual backend servers, set max_fails and fail_timeout values, and configure other parameters specific to each server.

Load Balancing with Least Connection:

http {
    upstream backend {
        least_conn;
        server backend1.example.com;
        server backend2.example.com;
        server backend3.example.com;
    }
    
    server {
        listen 80;
        
        location / {
            proxy_pass http://backend;
        }
    }
    
    # Additional configuration...
}

The least_conn directive ensures that requests are distributed to the backend server with the fewest active connections.

Some commonly used parameters include:

least_conn with the backup parameter: This designates a server as a backup in case all other servers become unavailable or reach a maximum connection threshold.
least_conn with the down parameter: This marks a server as temporarily down and prevents new connections from being established.
least_conn with the max_fails and fail_timeout parameters: This allows you to set the maximum number of failed attempts and the timeout period before considering a server as unavailable.

Save and Test Configuration:

After making the necessary configuration changes, save the file and check the configuration for any syntax errors:

sudo nginx -t

If the configuration is valid, restart or reload Nginx:

sudo service nginx restart

Monitor and Scale:

Once the load balancer is set up, you can monitor its performance using Nginx's built-in monitoring tools or third-party solutions. You can scale the backend servers horizontally by adding or removing servers from the upstream group without impacting the load balancer's configuration.

Additionally, you may consider configuring health checks (proxy_next_upstream) to ensure that Nginx only forwards requests to healthy backend servers.
It's crucial to fine-tune the load balancing configuration and monitor the system's behavior to optimize performance and ensure high availability and reliability of your application.