John, thanks for your questions.
> Isn’t that incredibly insecure?
To make the TeamCity server created by template production ready you should configure HTTPS endpoint for this vm. At the moment template does not provide such automation and we’ve the issue to implement it: https://github.com/JetBrains/teamcity-azure-template/issues/5
> I guess I could try creating TeamCity VMs in other regions by trial and error but why isnt’ this working in UK South?
Currently ACI service is available in the limited number of regions where UK South is not listed at the moment: https://azure.microsoft.com/en-us/global-infrastructure/services/?products=container-instances With a time Microsoft could expand support for additional regions.