pitfall: proxy_pass with var requires proxy_redirect

[lcarva]

When a variable is used in proxy_pass directive, the location header is not longer adjusted. This causes the value coming from backend to make its way back to client. To get around this, simply set proxy_redirect.

This will not fix up location redirect:

location = /proxy/ {
    set $endpoint proxy.com;
    resolver 8.8.8.8 valid=10s;
    proxy_pass https://$endpoint/;
}

This will:

location = /proxy/ {
    set $endpoint proxy.com;
    resolver 8.8.8.8 valid=10s;
    proxy_pass https://$endpoint/;
    proxy_redirect https://$endpoint/ /;
}

You can define proxy_redirect on server context if used in multiple locations.
This a single line in docs that mention it:

The default parameter is not permitted if proxy_pass is specified using variables.

[DmitryFillo]

Good point, I will notice this in the documentation soon. Or you can send pull request :-)

[DmitryFillo]

@lcarva thank you :-)