Nginx configuration for 503 custom maintenance page

nginx-503.conf

server { 
 
    listen 80;
    # default catch-all domain 
    server_name  _ ;

    error_page 503 @503 ;
    #return 503 ;

    root   /var/www/htdocs/ ; 
    server_name_in_redirect  off;
    #rewrite rule for auto versioning
    rewrite ^/(css|js)/(.*)\.t([0-9].*)\.(css|js)$  /$1/$2.$4 ;
    try_files $uri $uri/ /index.php?q=$uri&$args;

    location @503 {
        #avoid redirect to built-in 503.
        try_files /site/503.html =503;
    }

    location ~* \.(js|css|png|jpg|jpeg|gif)$ {
        expires 30d ;
        break ;
    }       

    #pass all requests for php to fastcgi 
    location ~ \.php$ {
        try_files $uri =404;
        #change port on local m/c.
        fastcgi_read_timeout 600 ;
        fastcgi_pass 127.0.0.1:9100 ;
    }    
}