Configured

Opinionated utility to load a configuration from well defined layers into any type which can be deserialized by Serde using kebab-case.

First, values from the mandatory default configuration file at <CONFIG_DIR>/default.yaml are loaded.

Then, if the environment variable CONFIG_OVERLAYS is defined, its comma separated overlays (e.g. "prod" or "feat, dev") at <CONFIG_DIR>/<overlay>.yaml are loaded from left to right as overlays, i.e. adding or overwriting already existing values.

Finally environment variables prefixed with <CONFIG_ENV_PREFIX>__ and segments separated by __ (double underscores are used as segment separators to allow for single underscores in segment names) are used as final overlay.

Example

#[derive(Debug, Deserialize)]
#[serde(rename_all = "kebab-case")]
struct Config {
    foo: Foo,
    qux: Qux,
}

#[derive(Debug, Deserialize)]
#[serde(rename_all = "kebab-case")]
struct Foo {
    bar: String,
    baz: String,
}

#[derive(Debug, Deserialize)]
#[serde(rename_all = "kebab-case")]
struct Qux {
    quux: String,
    corge_grault: String,
}

#[test]
fn test_load() -> Result<(), Error> {
    env::set_var(CONFIG_DIR, "test-config");
    env::set_var(CONFIG_OVERLAYS, "feat, dev");
    env::set_var("APP__QUX__CORGE_GRAULT", "corge-grault-env");

    let config = Config::load()?;

    assert_eq!(config.foo.bar.as_str(), "bar");
    assert_eq!(config.foo.baz.as_str(), "baz-dev");
    assert_eq!(config.qux.quux.as_str(), "quux-feat");
    assert_eq!(config.qux.corge_grault.as_str(), "corge-grault-env");

    Ok(())
}

Attribution

This utility is built on top of the fantastic Config library.

License

This code is open source software licensed under the Apache 2.0 License.