Thanks.
Actually the redis error was/maybe a red herring.
I can now access the welcome splash once I fixed up access to “avatars.discourse.org”
The problem for me is that my corporate DNS servers resolve only internal hosts.
nginx expects to resolve the above domain, but cannot - hence ngnix crashes 
This was the key - Restarting container when internet is down causes discourse to fail - #4 by sam
I progress by passing docker args to set /etc/hosts. Its not a production solution though…