nginx "env" directive is not allowed here

I use nginx with docker-compose and want docker-compose to pass SERVER_NAME to nginx as an environment variable. I created the following nginx configuration file:

myconf.conf:

# Environment variables are used to dynamically set SERVER_NAME
# from docker-defined environment variable. This logic  is stolen from:
#
# https://docs.apitools.com/blog/2014/07/02/using-environment-variables-in-nginx-conf.html
# https://github.com/wantedly/nginx-image-server/blob/master/files/nginx.conf

env SERVER_NAME;

upstream django {
    server workflows-django:8000;
}

server {
    listen 80;
    perl_set $server_name_from_env 'sub { return $ENV{"SERVER_NAME"}; }';
    server_name $server_name_from_env;
    return 301 https://$server_name$request_uri;
}

server {
    listen 443 ssl;
    perl_set $server_name_from_env 'sub { return $ENV{"SERVER_NAME"}; }';

    server_name $server_name_from_env;
    ssl_certificate /etc/ssl/private/bostongene.crt;
    ssl_certificate_key /etc/ssl/private/bostongene.key;
    charset utf-8;

    client_max_body_size 75M;

    location /media {
        alias /srv/workflows/media;
    }

    location /static {
        alias /srv/workflows/static;
    }

    location / {
        # We can talk to upstream django either via uwsgi or just http proxy

        # uwsgi:
        uwsgi_pass django;
        include /etc/nginx/uwsgi_params;


        # http proxy:
        #proxy_set_header Host $host;
        #proxy_pass http://django
    }
}

For some reason, nginx is cursing about that env directive:

2016/08/26 13:02:39 [emerg] 1#0: "env" directive is not allowed here in /etc/nginx/sites-enabled/default:7

Here's my Dockerfile, where you can see that this config is used as nginx default site:

Dockerfile:

FROM debian:latest

RUN apt-get update && apt-get install -y nginx \
                        ca-certificates \
                        gettext-base

COPY myconf.conf /etc/nginx/sites-available/default
COPY myconf.crt /etc/ssl/private/
COPY myconf.key /etc/ssl/private/

# forward request and error logs to docker log collector
RUN ln -sf /dev/stdout /var/log/nginx/access.log \
    && ln -sf /dev/stderr /var/log/nginx/error.log

EXPOSE 80 443

CMD ["/usr/sbin/nginx", "-g", "daemon off;"]

Why?

ANSWER: let me exlain, what was the problem in detail. myconf.conf file was used as /etc/nginx/sites-available/default, which is NOT the root nginx config. The root nginx config isnginx.conf and it includes /etc/nginx/sites-available/default in http context:

http {

    ...
    ##
    # Virtual Host Configs
    ##

    include /etc/nginx/conf.d/*.conf;
    include /etc/nginx/sites-enabled/*;
}

so my env statement is in fact in http context, which is incorrect - it should be written in root context only.