Hi @sowe1! I'm not sure that ODK Central is currently compatible with what you're trying to achieve, but I wanted to ask more questions about your setup.
What version of ODK Central are you running? Based on your default.json, it looks like you're running one of the v1.3 versions. I ask because we made some improvements from v1.2 to v1.3 related to configuring custom database servers. See the forum topic about the v1.3 release for more information. (Note that we still need to document some of those changes.)
It's possible that your database configuration doesn't match what Central is expecting. It sounds like you stubbed out host in the default.json you uploaded here. Did you stub out other values? If so, what format do they follow? Do they contain non-alphanumeric characters?
Are you specifying a port? If so, that should be done by adding a separate port configuration.