Rails runs an app in one named environment at a time, chosen by the RAILS_ENV variable, and loads that environment's settings on boot. Three come by default:
- development reloads code after every change, shows detailed error pages and includes debugging tools like the web console.
- test runs the test suite against its own database, loads fixtures and rolls back each test's changes.
- production is tuned for performance. It loads all code once at boot, turns on caching and hides error details from users, so teams add error monitoring there.
# Check current environment
Rails.env.development? # true/false
Rails.env # "development"
# Environment-specific code
if Rails.env.production?
# Production-only code
end
Each environment has its own file in config/environments/ and its own section in config/database.yml. To add a custom environment such as staging, you create both yourself.
# Custom environments
RAILS_ENV=staging rails server
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