Working F5 load balance config for Rancher 2.0 HA

I’ve been trying to get a working F5 load balance configuration going for my Rancher 2.0 HA install but I keep getting this error:

400 Bad Request

The plain HTTP request was sent to HTTPS port
nginx/1.13.8

I’ve got a pcap of the request and it shows all 4 required headers are present. I’m running F5 11.6 which is supposed to handle websocket requests automatically so as far as I can tell I’ve satisfied Rancher’s proxy requirements. Incidentally, I configured Nginx as per the instructions and that works fine so it’s not a problem with the Rancher install.

Here’s the pcap:
GET / HTTP/1.1
Host: rancher.icwgrp.com
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:62.0) Gecko/20100101 Firefox/62.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,/;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate, br
Connection: keep-alive
Upgrade-Insecure-Requests: 1
Cache-Control: max-age=0
X-Forwarded-For: 10.25.11.126
X-Forwarded-Proto: https
X-Forwarded-Port: 443

Pcap of the response:
HTTP/1.1 400 Bad Request
Server: nginx/1.13.8
Date: Mon, 17 Sep 2018 17:22:59 GMT
Content-Type: text/html
Content-Length: 271
Connection: close
Strict-Transport-Security: max-age=15724800; includeSubDomains;

400 The plain HTTP request was sent to HTTPS port

400 Bad Request

The plain HTTP request was sent to HTTPS port
nginx/1.13.8

And here is the article I used to configure everything.
https://rancher.com/docs/rancher/v2.x/en/installation/ha/rke-add-on/layer-7-lb/This text will be blurred