Nginx variable in proxy pass does not work

Those two cases are not the same. If you use a variable, that value will replace the entire URI.

In this case:

location /site { 
    proxy_pass http://docker-site/site/mobile;
}

the URI /site/foo is passed upstream as /site/mobile/foo.

To use your variable, you can use a rewrite (see this document for details):

location /site { 
    rewrite ^/site(.*)$ /site/$myvariable$1 break;
    proxy_pass http://docker-site;
}

Or a regular expression location:

location ~ ^/site(.*)$ {
    proxy_pass http://docker-site/site/$myvariable$1;
}

The evaluation order of regular expression location blocks is significant. See this document for details.

Related