Many thanks for all the help so far Jay.
I do have another question 
At present I and setting several env vars in our deployment i.e. DISCOURSE_BACKUP_LOCATION=s3 and my understanding is Discourse will use that value rather than what has been set via the UI and hence stored in the site_settings table - is that correct? If yes, are there any tools/scripts available that would allow me to check what env vars are set and determine their site setting equivalent?
Why - I am looking to migrate a running Discourse instance and to help minimise the risk I wanted to not set the env vars for now incase I missed any in the new instance and had a detrimental impact on the new instance. My thought was I could check what is set in the current instance, create the relevant settings in the table, backup/restore to the new instance and then extract away to the env vars one at a time.
Logical - maybe not but I thought that would be the most common sense approach just incase an env var in the running instance is different/not supported in the new instance (running = old Discourse version, new = latest Discourse)