Setup dynamic upstream with nginx

Question

Suppose that i have to upstream source

upstream first {
}

upstream second {
}

And then in server block

map $geoip_country_code $is_china {
    default no;
    CN yes;
}

What I would like to achieve is if $is_china, use a different upstream

proxy_pass http://$preferred_host/;

I can't figure how to do this with nginx.

Answer 1

map might be just sufficient. Have you tried the following?

map $geoip_country_code $preferred_host {
    default first;
    CN      second;
}

Answer 2

Turn out I can use if in nginx

set $preferred_host http://first;
if ($is_china) {
    set $preferred_host http://second;
}

location / {
    proxy_pass $preferred_host/;
    ...
}