Environment configuration files in Ruby on Rails - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of environment configuration files in Rails?

They store settings that change depending on where the app runs, like development, test, or production. This helps the app behave correctly in each place.

beginner

Name the three default Rails environment configuration files.

development.rb, test.rb, and production.rb inside the config/environments directory.

intermediate

How does Rails decide which environment configuration file to use?

Rails uses the RAILS_ENV environment variable to pick the right config file. If not set, it defaults to development.

intermediate

Why should sensitive data not be stored directly in environment configuration files?

Because these files can be shared or pushed to public code repositories. Instead, use environment variables or encrypted credentials.

intermediate

What is the role of config/application.rb compared to environment config files?

config/application.rb holds settings common to all environments, while environment files hold settings specific to each environment.

Which file would you edit to change settings only for the production environment in Rails?

A config/environments/development.rb

B config/environments/production.rb

C config/application.rb

D config/database.yml

The production.rb file holds settings specific to the production environment.

What does Rails use to determine the current environment?

A config/environment.rb file

B config/routes.rb

C Gemfile

D RAILS_ENV environment variable

Rails checks the RAILS_ENV variable to know which environment to run.

Where should you put settings that apply to all environments in a Rails app?

A config/application.rb

B config/environments/test.rb

C config/environments/production.rb

D config/secrets.yml

config/application.rb holds shared settings for all environments.

Why avoid putting passwords directly in environment config files?

A Passwords must be in the database only

B Rails does not support passwords in config files

C They might be exposed in version control

D It slows down the app

Storing passwords in config files risks exposing them if the code is shared.

If RAILS_ENV is not set, which environment does Rails use by default?

A development

B test

C production

D staging

Rails defaults to the development environment if RAILS_ENV is missing.

Explain how Rails uses environment configuration files to manage different settings for development, test, and production.

Think about how the app changes behavior depending on where it runs.

Describe best practices for handling sensitive information in Rails environment configurations.

Consider what happens if your code is shared publicly.

Practice

1. What is the main purpose of environment configuration files in a Rails application?

easy

A. To set different settings for development, test, and production environments

B. To store user data securely

C. To define database schemas

D. To write application business logic

Solution

1. Step 1: Understand environment files role

   Environment files in Rails are used to configure how the app behaves in different situations like development or production.

2. Step 2: Match purpose to options

   Only To set different settings for development, test, and production environments describes setting different configurations for each environment, which is the main purpose.

3. Final Answer:

   To set different settings for development, test, and production environments -> Option A

4. Quick Check:

   Environment files configure settings per environment [OK]

Hint: Think: different setups for dev, test, prod [OK]

Common Mistakes:

• Confusing environment files with database schema files
• Thinking environment files store user data
• Assuming business logic is set here

2. Which file path correctly points to the production environment configuration in a Rails app?

easy

A. config/production/environment.rb

B. config/environments/production.rb

C. config/environment/production.rb

D. config/environments.rb/production

Solution

1. Step 1: Recall Rails environment file location

   Rails stores environment configs inside the config/environments directory.

2. Step 2: Identify correct file name for production

   The production environment file is named production.rb inside that folder.

3. Final Answer:

   config/environments/production.rb -> Option B

4. Quick Check:

   Production config file path = config/environments/production.rb [OK]

Hint: Look for config/environments/[env].rb [OK]

Common Mistakes:

• Swapping folder and file names
• Using incorrect folder order
• Adding extra file extensions

3. Given this code in config/environments/development.rb:

Rails.application.configure do
  config.cache_classes = false
  config.eager_load = false
end

What effect does this configuration have when running the app in development?

medium

A. Eager loading loads all code at startup, slowing boot time

B. Classes are cached, improving performance but requiring server restart

C. Classes reload on each request, speeding up development changes

D. Caching is enabled, so data is stored permanently

Solution

1. Step 1: Understand config.cache_classes = false

   This means Rails reloads classes on every request, so code changes show immediately without restarting.

2. Step 2: Understand config.eager_load = false

   Eager loading off means Rails does not load all code at startup, which is typical for development to save boot time.

3. Final Answer:

   Classes reload on each request, speeding up development changes -> Option C

4. Quick Check:

   cache_classes false means reload classes each request [OK]

Hint: cache_classes false means reload code on every request [OK]

Common Mistakes:

• Confusing cache_classes false with caching data
• Thinking eager_load false means eager loading is on
• Assuming classes are cached in development

4. You added this line to config/environments/production.rb:

config.consider_all_requests_local = true

But you still don't see detailed error pages in production. What is the likely problem?

medium

A. Rails does not support detailed errors in production at all

B. The line should be in development.rb, not production.rb

C. You need to restart the server for changes to take effect

D. The setting is overridden by another config file or environment variable

Solution

1. Step 1: Understand consider_all_requests_local

   This setting controls if Rails shows detailed error pages. True means show detailed errors.

2. Step 2: Check why it might not work in production

   Often other configs or environment variables override this setting, preventing detailed errors.

3. Final Answer:

   The setting is overridden by another config file or environment variable -> Option D

4. Quick Check:

   Overridden config blocks detailed errors [OK]

Hint: Check for overrides or env variables blocking changes [OK]

Common Mistakes:

• Assuming detailed errors never show in production
• Not restarting server after config changes
• Putting setting in wrong environment file

5. You want to disable asset debugging only in the test environment without affecting development or production. Which change correctly achieves this in Rails?

medium

A. Add config.assets.debug = false inside config/environments/test.rb

B. Add config.assets.debug = false inside config/environments/production.rb

C. Add config.assets.debug = false inside config/application.rb

D. Add config.assets.debug = false inside config/environments/development.rb

Solution

1. Step 1: Identify environment-specific config location

   To change behavior only in test, put config in config/environments/test.rb.

2. Step 2: Set assets.debug to false in test environment

   Adding config.assets.debug = false in test.rb disables asset debugging only for tests.

3. Final Answer:

   Add config.assets.debug = false inside config/environments/test.rb -> Option A

4. Quick Check:

   Environment-specific config goes in matching environment file [OK]

Hint: Put config in matching environment file to isolate changes [OK]

Common Mistakes:

• Changing config in wrong environment file
• Changing config in application.rb affects all environments
• Forgetting to restart server after changes