The setup was based on this guide.
The server is setup with multiple Discourse installs running under a single Nginx instance with separate vhosts.
For reference each vhost takes this form:
server {
listen 80;
# change this
server_name my-discourse-site.com;
client_max_body_size 100M;
location / {
proxy_pass http://unix:/var/discourse/shared/*****/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;
}
}