default

server {
        client_max_body_size 500M;
        passenger_friendly_error_pages on;
        listen 80 default_server;
        listen [::]:80 default_server ipv6only=on;

        server_name sempermedusa.com;
        passenger_enabled on;
        rails_env    production;
        root         /home/deploy/sites/sempermed/current/public;

        rewrite ^(/blog)(.*)$   http://sempermedusa.com:81 permanent;

        # redirect server error pages to the static page /50x.html
        error_page   500 502 503 504  /50x.html;
        location = /50x.html {
            root   html;
        }
}

question

I've got a rails site at sempermedusa.com and I'm trying to have sempermedusa.com/blog point to the wordpress site. This rewrite rule:
rewrite ^(/blog)(.*)$   http://sempermedusa.com:81 permanent;
does work, but the problem is the url in address bar shows http://sempermedusa.com:81 instead of http://sempermedusa.com/blog.

wordpress

server {
        listen 81 default_server;
        listen [::]:81 default_server ipv6only=on;

        root /var/www/html;
        index index.php index.html index.htm;

        server_name sempermedusa.com;

        location / {
                # try_files $uri $uri/ =404;
                try_files $uri $uri/ /index.php?q=$uri&$args;
        }

        error_page 404 /404.html;

        error_page 500 502 503 504 /50x.html;
        location = /50x.html {
                root /usr/share/nginx/html;
        }

        location ~ \.php$ {
                try_files $uri =404;
                fastcgi_split_path_info ^(.+\.php)(/.+)$;
                fastcgi_pass unix:/var/run/php5-fpm.sock;
                fastcgi_index index.php;
                include fastcgi_params;
        }
}