Yay!! It’s done! IP’s are now showing correctly in the access log 
For some reason the spacing messed up in the snippet above, here it is for anyone who might need it in future:
run:
- replace:
filename: /etc/nginx/conf.d/discourse.conf
from: "types {"
to: |
set_real_ip_from 172.17.0.0/24;
real_ip_header X-Forwarded-For;
real_ip_recursive on;
types {
