Config from the environment

Config lives in the environment

Your server needs to know things that change between your laptop and production: which port to listen on, the database URL, the secret used to sign login tokens. Where do those values come from?

The answer the industry settled on is 12-factor config: read settings from environment variables, not from files baked into the build. Same binary runs everywhere; the environment tells it how. No secrets in git, and switching from dev to prod is just different env vars — no recompile.