Configs

config files

Settings live outside the code in files under config/. Each file groups values by application name, so ports, hosts, and feature flags stay visible in one place instead of hiding inside modules.

import Config config(:hello, greeting: "hi")

Per-environment

Development and production rarely share settings. Keep common values in config/config.exs and overrides in files like config/dev.exs and config/prod.exs, selected by the current environment.

import Config import_config("#{config_env()}.exs")

runtime.exs

Values baked at build time cannot follow the deploy environment. The file config/runtime.exs runs at boot, so it reads the machine around it and configures the release accordingly.

port = System.get_env("PORT", "4000") config(:hello, port: port)

Application.fetch_env!

Read required settings with a strict call that raises when the key is missing. A loud boot failure beats a quiet wrong default that surfaces hours later.

Application.fetch_env!(:hello, :greeting)

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Article author: Arthur Isaev