La última IP muestra la dirección IP del proxy inverso

[schleifer (Andrew Schleifer)]

The nginx running in the container does not trust headers set by the proxy.

X-Forwarded-For proxy tag not recognized by Discourse?

Take a look at the templates/cloudflare.template.yml file. Basically, you need to insert set_real_ip_from directives for the full list of load balancer IPs.