Nginx reverse proxy set up behind a elastic load balancer and in front of a Play web app. Redirects http to https.

nginx.conf

# This sets up a nginx reverse proxy behind a load balancer and in front of
# the Play web app. The setup is illustrated as the following:
#
# LB:80  ==> RP:80   ==> (Redirect to https)
# LB:443 ==> RP:8080 ==> Backend:9001
#
# LB -- Load Balancer
# RP -- Reverse Proxy
#
# IMPORTANT: Remove the line `include /etc/nginx/sites-enabled/*` from this config
#
http {

  ##
  # Reverse proxy
  ##

  proxy_buffering off;
  proxy_redirect off;
  proxy_http_version 1.1;
  proxy_set_header X-Real-IP $remote_addr;
  proxy_set_header X-Scheme $scheme;
  proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
  proxy_set_header Host $host;
  proxy_next_upstream error timeout invalid_header http_500 http_502 http_503 http_504;

  upstream dashboard-backend {
    server localhost:9001;
  }

  server {
    listen 8080;
    server_name dashboard.synapse.org;
    location / {
      proxy_pass http://dashboard-backend;
    }
  }

  ##
  # Redirect http to https
  ##

  server {
    listen 80;
    return 301 https://$host$request_uri;
  }
}

Any idea why you have to set up proxy_buffering off;?
I had to do it on my server config because of some inconsistent issues but have no idea why it worked.