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Environment Overrides

Override any configuration value using environment variables.

Basic Syntax

Environment variables use the pattern:

{PREFIX}_{KEY}=value

For your config:

class MyApp::Config < MywayConfig::Base
  config_name :myapp
  env_prefix  :myapp  # This sets the prefix
  # ...
end

Override values:

MYAPP_LOG_LEVEL=warn
MYAPP_DEBUG=true
MYAPP_MAX_CONNECTIONS=50

Nested Values

Use double underscore (__) for nested keys:

# Override database.host
MYAPP_DATABASE__HOST=custom-db.local

# Override database.port
MYAPP_DATABASE__PORT=5433

# Override api.headers.content_type
MYAPP_API__HEADERS__CONTENT_TYPE=text/plain

Priority Order

Environment variables have high priority. Values are loaded in order:

  1. Bundled defaults (lowest)
  2. Environment-specific overrides from YAML
  3. XDG user config
  4. Project config
  5. Environment variables (high priority)
  6. Constructor overrides (highest)

Type Coercion

Values are automatically coerced based on the default type:

defaults:
  port: 5432        # Integer
  debug: false      # Boolean
  timeout: 30.5     # Float
  log_level: :info  # Symbol

MYAPP_PORT=9999           # Becomes Integer 9999
MYAPP_DEBUG=true          # Becomes Boolean true
MYAPP_TIMEOUT=60.0        # Becomes Float 60.0
MYAPP_LOG_LEVEL=warn      # Becomes Symbol :warn

Examples

Running with Overrides

# Development with custom database
MYAPP_DATABASE__HOST=localhost MYAPP_DATABASE__PORT=5433 ruby app.rb

# Production-like settings locally
RACK_ENV=production MYAPP_DATABASE__HOST=prod-db.local ruby app.rb

In Docker

ENV MYAPP_DATABASE__HOST=db
ENV MYAPP_DATABASE__PORT=5432
ENV MYAPP_LOG_LEVEL=info

In docker-compose

services:
  app:
    environment:
      - RACK_ENV=production
      - MYAPP_DATABASE__HOST=db
      - MYAPP_DATABASE__PORT=5432

In Heroku

heroku config:set MYAPP_DATABASE__HOST=your-db.herokuapp.com
heroku config:set MYAPP_LOG_LEVEL=warn

Checking Values

Verify environment variable overrides are working:

config = MyApp::Config.new

puts "Database host: #{config.database.host}"
puts "From env: #{ENV['MYAPP_DATABASE__HOST']}"

Debugging

If values aren't being picked up, check:

  1. Prefix matches - env_prefix in your class must match
  2. Double underscore - Nested keys need __
  3. Case sensitivity - Environment variables are uppercase
  4. Load order - Config class must be loaded after env vars are set

Next Steps