I am experimenting with containing website using Docker, and I managed to get half of it work. Website works correctly with Nginx with this config:

server {
    listen 80;
    server_name example.com;
 location / {
        proxy_pass http://backend_server/;
        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; 
    }
}
upstream backend_server {
    server 127.0.0.1:8000;

}

But when I try to add php snippet

 location ~ .php$ {
        proxy_pass http://localhost:8081;
        include snippets/fastcgi-php.conf;
        fastcgi_pass unix:/run/php/php8.1-fpm.sock;  
        fastcgi_param PATH_INFO $fastcgi_path_info;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
    }

it does not work, cannot find any .php file.

I tried with

        proxy_pass http://backend_server/;
        proxy_pass http://localhost:8000$uri;

But it does not matter.