How can query string parameters be forwarded through a proxy pass with nginx

When using Nginx as a proxy server, passing query string parameters from the client to the upstream server (e.g., an application server) is a common requirement. Nginx automatically passes the query string parameters in the request to the upstream server by default. This is because when a request is proxied, the entire request line (including the URI and query string) is forwarded.

The following is a basic Nginx configuration example demonstrating how to set up a proxy for an application server and automatically include the query string:

nginx
server {
    listen 80;

    server_name example.com;

    location / {
        # Proxy settings to forward requests to the backend application server
        proxy_pass http://backend_server;

        # The following are common proxy settings to ensure proper handling of request and response headers
        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, the proxy_pass directive defines the address of the upstream server. When a client sends a request to Nginx, if the request includes a query string, Nginx will automatically forward the entire request URI (including the query string) to http://backend_server.

For example, if a client requests http://example.com/search?q=openai&lang=en, Nginx will proxy this request to http://backend_server/search?q=openai&lang=en, including the query string ?q=openai&lang=en.

If you need to modify the query string or perform special handling based on it, you can use the rewrite directive or the $args variable. Here is an example using the rewrite directive to modify the query string:

nginx
server {
    listen 80;

    server_name example.com;

    location / {
        # Check the request's query string and add 'lang=en' if 'lang' parameter is missing
        if ($args !~ "lang=") {
            set $args "${args}&lang=en";
        }

        # Forward the modified request to the backend server
        proxy_pass http://backend_server;

        # Other proxy settings...
    }
}

In this example, if the original request lacks the lang parameter, Nginx will add lang=en to the query string and forward the modified request to the upstream server.