Load balance with Nginx and node.js

how can i load balance my app (node.js).

At moment i have 2 versions of my application users will be routed depending on

what version they belong to. (Everything works good)

Now i want to load balance each version.

ex
I want "v1" to run under :3000 and 3001, 3002.
How can i do that without interfere with my current solution?

Current code.

map $cookie_version $mybackend {
 default "127.0.0.1:3000";
 "v1" "127.0.0.1:8080";
 "v2" "127.0.0.1:3000";
}
...
location / {
 proxy_pass http://$mybackend;
}
...
location ~ ^/(?<cver>v[12])/ {
 ...
 add_header Set-Cookie "version=$cver;Domain=localhost;Path=/";
 rewrite ^/v[12]/(.*)$ /$1 redirect;
}

Thanks.