Discourse itself is HTTP, (my own) nginx in front of it does https:
location @fallback {
proxy_pass http://unix:/sites/websites/discourse/discourse2/shared/standalone/nginx.http.sock:;
proxy_set_header Host $http_host;
proxy_http_version 1.1;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
}