How to use Umbrella projects properly

I would suggest avoiding configuring your app via config.exs - this is a build time configuration. Granted, some libraries make it harder than others, but you should generally favour runtime configuration. Seems like Kaffe supports that with start_link/4 - pull it from ENV, not config.exs.

Given that, it seems umbrella apps might not be what you need:

Don’t drink the kool aid

Umbrella projects are a convenience to help you organize and manage multiple applications. While it provides a degree of separation between applications, those applications are not fully decoupled, as they share the same configuration and the same dependencies.

The pattern of keeping multiple applications in the same repository is known as “mono-repo”. Umbrella projects maximize this pattern by providing conveniences to compile, test and run multiple applications at once.

If you find yourself in a position where you want to use different configurations in each application for the same dependency or use different dependency versions, then it is likely your codebase has grown beyond what umbrellas can provide.

I think you’d be good with just a common lib and multiple projects.

@stefanchrobot Thanks for the hints … I think I will go with the multiple projects aproach. I am now taking a look into distillery to try to figure how to create releases with multiple projects … if that’s even possible.

Regarding configuration, and sorry if the question is too dumb or basic but I am just starting to learn the Elixir environment, by favour runtime configuration you mean to use a config/releases.exs file and read values from environment variables there?
I was wondering if there isn’t any way to load configuration in Elixir similar to configmaps in k8s, that is from a file.

Anyway, thanks again for your time.

What would be the benefit of creating a release with multiple projects? I’d go with a release per project and would also suggest Elixir’s releases as they are simpler.

config/config.exs and friends (except for config/releases.exs) are build-time configuration. So if you read ENV there, it’s going to be baked into the app with whatever the value was at the compile stage. This is where config/releases.exs comes in. The problem is that it’s used only by an app packaged as a release.

My personal approach and preference is to have the same flow in all cases (prod, dev and test). So my configs are mostly empty, except for things that are required to be configured at build-time. My release config is empty as well. I pushed all config to relevant places much like as suggested by Saša Jurić in his blog post. For dev and test I’m populating ENV using .env files, in prod the ENV is populated by the platform (Gigalixir, Render, etc.).

EDIT:

See also: Add config/runtime.exs · Issue #9884 · elixir-lang/elixir · GitHub