Confispex - a schema for runtime variables

Hi all!

Confispex is a tool which allows defining specs for runtime configuration, cast values according to specified types and inspect them.

We needed a tool for managing complexity of runtime configuration. We have a lot of environment variables in monolithic application. > 150+ to be more precise. In such a situation runtime.exs quickly becomes polluted with badly designed anonymous functions which convert data to needed Elixir terms. Also, these functions have bad error reporting, because in a case of exception stacktrace isn’t available in runtime.exs file. Environment variable names are flat, it is essential to want to categorize them. We can’t switch to yaml-like configuration file, because existing infrastructure forces using environment variables. Variables can be used only in certain env, can have aliases, can be required/optional and this is needed to be documented somehow. The easiest way to specify that variable is required is by calling System.fetch_env!/1, but to see all required variables if they aren’t documented, you have to run application n times when n is a number of required variables. The team uses direnv in development and have to keep a template of .envrc file up-to-date for newcomers.

So, how confispex helps with issues mentioned above?

Elixir 1.11 allows running application code in runtime.exs, so confispex uses a schema defined in your application code to cast values to Elixir terms. Errors should not be reported immediately, but only when you ask a report. If confispex can’t cast value from store or default value to specified type, then nil is returned. Think about it as an advanced wrapper around System.get_env/1. Also, there is a mix task to generate a .envrc template from schema.

Check Getting Started page to see how it works.