NGinx configuration to proxy Grunt from a subdir

grunt.site

    set $front_port "9000";
    set $front_host "10.0.2.2";
 
    location @proxy_to_front {
        proxy_set_header Host $http_host;
        proxy_redirect off;
        proxy_set_header X-Real-IP         $remote_addr;
        proxy_set_header X-Forwarded-For   $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Protocol   $scheme;
        rewrite  ^/app(.*)  $1 break;
        proxy_pass http://$front_host:$front_port;
    }
 
    location /app {
        try_files $uri @proxy_to_front;
    }