This is terrible advice. Code and config should be separate. Otherwise you can't deploy the same code to a different environment.
If you want to run local environment you can simply create your own configuration.
I don't really see what you gain by moving configuration files into a separate repository.
Externalizing config forces you to cleanly handle local environments as well. There's nothing special about them.
I generally recommend having an env.example file listing out required environment variables with sensible local defaults. This eases onboarding a new developer or even an existing developer on a new machine.
> I don't really see what you gain by moving configuration files into a separate repository.
Because config and code should be kept separate. Updating the database that your production app is using is not a code change. It's a config change.
Setting up a new CI environment should not require pushing new code.
If you have a production issue in version X, separating code and config allows you to reproduce it using an isolated database/mq/foobar service. It's exactly the same code.
I can always grab the build from production and run it locally with the modified config.
Which production env? Which datacenter? Which database cluster? &c
The deployment should take care of generating configs, they shouldn't be hardcoded or stored anywhere imho.
Sure deployment can generate configs but it has to take it from somwhere. So you need a database preferably with versioning and encryption. It's also nice if you know which settings are used in specific builds so you can go back and debug past production issues.
Of course for larger teams and deployments it makes sense to develop and maintain this infrastructure. But since we already have git, why not just use it.
The Twelve-Factor Methodology is a sensible set of guidelines/defaults for building a modern app, as written by Heroku.
Don't blindly follow it As It Was Written without thinking. Seriously, do what works. Use your brain. Using this statement as an argument against other methods is sending the wrong message.
In this case, we have code and [configuration] data. The data can and will vary considerably while reusing the same code. They should be separate so data changes don't require recompilation. Further, any change of code can change its behavior. Better to have code that's already vetted via review and testing to handle specific types of input data. That way you can keep changing the data without re-assessing the code. There's also a minor benefit in efficiency when you can re-use binaries already created and integration tested while just generating new configuration data. Those minor things can add up if you're constrained in CPU/memory.
This is the complete opposite of my experience. We deploy new code to production 10 times per day and change configuration a couple of times per month.
What do you keep in configuration that changes this often?