nginx is not defining $scheme

Question

I just upgraded from nginx 1.4.1 to 1.8.0 (along with an upgrade to Phusion Passenger 5.0.13). With that change the $scheme variable from our configuration no longer seems be set.

The nginx configuration looks something like this:

server {
     listen 80;
     listen 443;
     ssl on;

     server_name app.example.com;

     passenger_enabled on;
     passenger_env_var HTTP_X_FORWARDED_PROTO $scheme;

     proxy_set_header X-Forwarded-Proto $scheme;

     ...
}

When I inspect request.env['HTTP_X_FORWARDED_PROTO'] or request.headers['X-Forwarded-Proto'] in the Rails application, I get the literal "$scheme", not "http" or "https".

I have tried both proxy_set_header and passenger_set_header and have the same results.

Answer 1

This issue here is that I was setting the environment variable as well as the header. Removing this line fixed this:

passenger_env_var HTTP_X_FORWARDED_PROTO $scheme;

This is caused by the fact that passenger_env_var is evaluated at the beginning of the application rather than on each request. Because $scheme isn't defined at that time it was set there.

I don't know why the header was also pre-set but I suspect it has something to do with the fact that Passenger tries to sync the headers and environment variables to mimic a CGI environment.