How to use phpBB, phpMyAdmin with Unicorn and nginx?

I used the 1-Click Ruby on Rails on Ubuntu 14.04 Image and this guide to setup my rails app: https://www.digitalocean.com/community/tutorials/how-to-use-the-1-click-ruby-on-rails-on-ubuntu-14-04-image . Then, I used the the PHP guide https://www.digitalocean.com/community/tutorials/how-to-install-linux-nginx-mysql-php-lemp-stack-on-ubuntu-12-04 to install PHP.

On my previous shared host, I ran the phpBB forum from inside the rials public directory. The Apache .htaccess file had an entry to turn off the rails rewrite rule.

How can I achieve this with nginx? Right now when I go to www.mydomain.com/forum , rails returns a 404 error. How can I tell nginx to server php inside my /home/myrailsapp/public/forum ? Is there a better way? Below is my nginx config file.

server {
        listen   80;
        root /home/myrailsapp/public;
        server_name my_ip;
        index index.htm index.html index.php;

        location / {
                try_files $uri/index.html $uri.html $uri @app;
        }

        location ~* ^.+\.(jpg|jpeg|gif|png|ico|zip|tgz|gz|rar|bz2|doc|xls|exe|pdf|ppt|txt|tar|mid|midi|wav|bmp|rtf|mp3|flv|mpeg|avi)$ {
                        try_files $uri @app;
        }

        location @app {
                proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
                proxy_set_header Host $http_host;
                proxy_redirect off;
                proxy_pass http://app_server;
        }
        # pass the PHP scripts to FastCGI server listening on the php-fpm socket
        location ~ \.php$ {
                try_files $uri =404;
                fastcgi_pass unix:/var/run/php5-fpm.sock;
                fastcgi_index index.php;
                fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
                include fastcgi_params;
        }
}