Routed traffic with cookies Nginx - node.js

Question

first time i'm trying to setup nginx.
I have following problem i would like to solve.
I have two versions of backend v1 and v2.
User is routed to "/v2" (proxy_pass '127.0.0.1:3000;')
Traffic tru "/" (javascript + sockets) has be routed to the same server '127.0.0.1:3000;' by looking at the cookie.
Heres my problem the cookie doesn't exists and therefore 404 will be returned
Any suggestion?
map $cookie_version $site_version {
default "";
"v1" "version=v1;Domain=localhost;Path=/";
"v2" "version=v2;Domain=localhost;Path=/";
}
server {
listen 8081;
server_name localhost;
location / {
if ($cookie_version ~* "v1") {
proxy_pass http://127.0.0.1:8080;
}
if ($cookie_version ~* "v2") {
proxy_pass http://127.0.0.1:3000;
}
}
location /v1 {
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection "upgrade";
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header Host $host;
proxy_http_version 1.1;
set $cookie_version "v1";
add_header Set-Cookie $site_version;
rewrite ^/v1(.*) /$1 break;
proxy_pass http://127.0.0.1:8080;
}
location /v2 {
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection "upgrade";
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header Host $host;
proxy_http_version 1.1;
set $cookie_version "v2";
add_header Set-Cookie $site_version;
rewrite ^/v2(.*) /$1 break;
proxy_pass http://127.0.0.1:3000;
}
}

Answer 1

First of all, read why if is evil http://wiki.nginx.org/IfIsEvil. Use map instead.
My suggestion:
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;
}