File-based configs are a troublesome abstraction: they package unrelated concerns into a rigid document whose form must take a particular, application-dependent

File-based configs are a troublesome abstraction: they package unrelated concerns into a rigid document whose form must take a particular, application-dependent shape, and the assembly and disassembly of that document essentially becomes an API where key-value pairs are mixed with complex glue code. The application has to do this internally, but anyone who's generating their configs are also doing parts of this externally. Templates try to bandage over that by drilling down the abstraction to key-value pairs themselves. And imperative constructs that sneak into templating languages are an artifact of wanting to gain expressiveness without losing the benefits of declarative form -- but really, the two are at odds. YAML is a red herring -- we had the same headaches with XML a decade prior. The problem is always that there's relationships among the data (or even multiple instances of the config) that we care about, but that the structure of a single config file at rest cannot model. Databases -- let's say, an SQL one -- are actually among the better solutions, because they allow the universe of config items to live in structured places without overspecifying the exact form the data must take when serialized into a file. Then, data can be normalized where it makes sense to avoid repetition and introduce propagation. An SQL database gives all the tools needed to accomplish this, using mostly declarative code. Databases in a KV sense are often used for configuration, and SQLite's rise has increased richly structured configs that are specified at a higher level than what's typically done with other serialization formats, but the full approach has not caught on outside big enterprise systems and complex applications. Which is a shame, because it's hardly more complex than the current awkward pairing of a full serializer and a templating engine.