Allow configuration from a specific file?

[johanhaleby]

Would it make sense to be able to load configuration not only from the environment but also from a file in Duct? I.e. when my uberjar is created I'm looking for something like this:

$ java -jar uberjar.jar --config ~/my-config

Background:

I'm trying to use ConfigMaps in Kubernetes with an application developed in Clojure using Duct. Kubernetes doesn't support specifying environment variables from a config map that doesn't match regex \.?[a-z0-9]([-a-z0-9]*[a-z0-9])?(\.[a-z0-9]([-a-z0-9]*[a-z0-9])?)*, which means that you cannot expose environment variables containing "special characters" this way (for example a \). Another way that is supported by Kubernetes is expose a config map as a file. Which means that if I somehow could instruct my uberjar to load properties from a file of my choice I would be able to get things to work without having to hack things.

[weavejester]

Configurations in Duct are just maps. You can meta-merge configurations from any source you want.

[johanhaleby]

Right, so essentially my question is whether or not this would be something that should be available by default (In Java I'm used to spring boot which supports loading configuration from a variety of different sources by default)? But I do understand if this is not desirable from Duct's perspective (since might increase the complexity of duct's code) but I just want to make sure that I'm not missing anything.

[weavejester]

I don't think offering multiple configuration sources by default as being a good idea. Adding a new configuration source should be one or two lines of code, and I don't think a template is needed for that. Better to have a single, sensible default - in this case environment variables - but make it trivial for users to use any source that produces a map of data.

[johanhaleby]

Would it make sense (and be possible) to create a profile that would add support for this? If so maybe I could help out.

[weavejester]

Add support for what? Kubernetes' ConfigMaps? I think that's a little too niche to warrant a profile.

[johanhaleby]

No no, I meant support for loading configuration from a user specified file. But the more I think of it the less sense it makes.. Thanks for your feedback, I'll close the issue.

[weavejester]

Well, that should only be a couple of lines of code. e.g.

(def file-config
  (edn/read-string (slurp "config.edn")))

Substituting edn/read-string with whatever configuration library you want. The <project>.config namespace is designed to hold static configurations loaded at startup, be it from a file, the environment, or something more exotic.

[johanhaleby]

thanks!