config: methods to achieve 12factor-ness?

[dpkirchner]

I like what I have read on the 12factor.net site but one concept in particular stands out as unclear, perhaps incomplete: config.

The site recommends using individual environment variables instead of sets of environment variables grouped in to environments (e.g. production, staging). However, the site also recommends that the development and production environments be kept as similar as is possible, suggesting that there must be some mechanism keeping at least the variable names in sync, if not the values, for consistent development environments. These two recommendations seem to be in conflict, or at least one could be clarified to support the other.

Are there practical examples demonstrating a way to manage environment variables without them being grouped in to environments or files that may inadvertently be committed to VCS?

[Rogach]

+1. That's very interesting point - I made a question on Programmes.SE about that, but didn't get sufficiently sane answers yet.