7. Configuration

Your app will run in three places: on your machine, in the tests and in production. Each needs different settings, like another database, other logs or another key. In this chapter you see how profiles handle that.

One base, one file per profile

config/
├── application.yaml         shared by every profile
├── application-dev.yaml     your machine
├── application-tests.yaml   the tests
└── application-prod.yaml    production

Preá always loads application.yaml, then the active profile's file on top of it. A profile's file only holds what is different.

Look at what the project already has:

application-dev.yaml

logging:
  level: debug
database:
  migrations:
    from_models: true # a model change becomes a migration at startup...
    on_start: true # ...that is applied right away

application-tests.yaml

server:
  mode: test
logging:
  level: error
database:
  url: ${TEST_DATABASE_URL}
  schema: create-drop

application-prod.yaml

server:
  mode: release
logging:
  format: json

• dev shows detailed logs and writes migrations from your models, as you've seen.
• tests uses the test database, and create-drop gives every test run fresh, empty tables.
• prod turns off debug output and writes logs as JSON, which log collectors read.

A key for the tests

The tests will need an API key too, and a fixed one is fine there. Add it to config/application-tests.yaml:

todo:
  api_key: tests-key-0123456789

The tests don't depend on anyone's .env, so they behave the same on every machine and in CI.

Pick a profile

The active profile comes from PREA_PROFILE, which your .env sets to dev. The CLI can override it:

prea run --profile prod

{"level":"INFO","msg":"prea: config loaded","profile":"prod"}
{"level":"INFO","msg":"prea: listening","addr":"[::]:8000"}
{"level":"SUCCESS","msg":"request","method":"GET","path":"/health","status":200,"latency":440708,"ip":"::1"}

The same app, now with JSON logs and in release mode. Stop it with Ctrl+C.

What goes where

Kind of setting	Where
the same everywhere, like the port	application.yaml
different per environment, like the log format	application-<profile>.yaml
secret, or different per machine, like passwords and keys	an environment variable, referenced as ${NAME}
part of the code, like which preás exist	preas/preas.go

Secrets never go in a YAML file. The files are committed, and the environment isn't.

What you learned

• application.yaml is the base, and each profile's file adds what is different.
• PREA_PROFILE, or --profile, picks the profile.
• Secrets come from the environment with ${NAME}.

Next: testing →