Every Rails app requires some kind of configuration:

• Rails Secret Token
• Database connection params
• 3rd party API keys
• Exception notification recipients
• …

Most of these should never be tracked in source control. So what do you do?

Store all configuration in environment variables. This approach works universally:

• no matter where you host: dedicated, VPS, heroku, AWS, …
• in all runtime modes: production, development and test.
• single server apps or large clusters.

So instead of hardcoding your database connection params in config/database.yml you pull them in via ERB and ENV vars like so:

development:
  adapter: postgresql
  encoding: unicode
  database: <%= ENV['POSTGRES_DATABSE'] %>
  pool:     <%= ENV['POSTGRES_POOLSIZE'] %>
  username: <%= ENV['POSTGRES_USERNAME'] %>
  password: <%= ENV['POSTGRES_PASSWORD'] %>

The Figaro gem is a great tool to manage your config:

• Install the gem: gem 'figaro'
• rails generate figaro:install - this will add a file config/application.yml which is ignored by git.
• add all your configuration parameters to config/application.yml.
• when your app boots up, all required ENV vars will be initialized.
• when you deploy to heroku, all ENV vars will be initialized there.

Here is an example for config/application.yml:

# Figaro application configuration
development:
  YOUR_APP_SECRET_TOKEN: 'haksdjfhalksdjfh60b84e71e...'
  POSTGRES_DATABASE: your_app_development
  POSTGRES_PASSWORD: pg_password
  POSTGRES_POOLSIZE: 5
  POSTGRES_USERNAME: pg_user_name
  REDIS_HOST: '127.0.0.1'
  REDIS_PORT: 6379
  TWITTER_CONSUMER_KEY: dfg345KJH...
  TWITTER_CONSUMER_SECRET: ZPFe78ku...

production:
  ...

test:
  ...