Logging and monitoring in Ruby on Rails - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to log an info message in Rails.

Ruby on Rails

Rails.logger.[1]("User signed in successfully")

Drag options to blanks, or click blank then click option'

Adebug

Berror

Cwarn

Dinfo

Attempts:

3 left

💡 Hint

Common Mistakes

Using debug level for normal info messages

Using warn or error for non-problematic events

The info method logs informational messages, which are useful for general application events.

2fill in blank

medium

Complete the code to set the log level to show warnings and above.

Ruby on Rails

Rails.logger.level = Logger::[1]

Drag options to blanks, or click blank then click option'

ADEBUG

BWARN

CINFO

DERROR

Attempts:

3 left

💡 Hint

Common Mistakes

Setting level to DEBUG logs too much information

Setting level to INFO logs less than required

Setting the log level to WARN means only warnings, errors, and fatal messages will be logged.

3fill in blank

hard

Fix the error in the code to log an error message with exception details.

Ruby on Rails

begin
  # some code
rescue => e
  Rails.logger.[1]("Error occurred: #{e.message}")
end

Drag options to blanks, or click blank then click option'

Adebug

Binfo

Cerror

Dwarn

Attempts:

3 left

💡 Hint

Common Mistakes

Using info or debug for error messages

Using warn which is less severe than error

The error method is used to log error messages, especially exceptions.

4fill in blank

hard

Fill both blanks to create a custom logger that writes to a file and sets the log level to debug.

Ruby on Rails

custom_logger = Logger.new([1])
custom_logger.level = Logger::[2]

Drag options to blanks, or click blank then click option'

A"log/custom.log"

BSTDOUT

CDEBUG

DINFO

Attempts:

3 left

💡 Hint

Common Mistakes

Using STDOUT instead of a file path for file logging

Setting log level to INFO instead of DEBUG

Creating a logger with a file path writes logs to that file. Setting level to DEBUG logs detailed messages.

5fill in blank

hard

Fill all three blanks to filter logs for requests with status code 500 or higher and log the path and status.

Ruby on Rails

ActiveSupport::Notifications.subscribe("process_action.action_controller") do |*args|
  name, start, finish, id, payload = args
  status = payload[[1]]
  path = payload[[2]]
  if status.to_i [3] 500
    Rails.logger.error("Error at #{path} with status #{status}")
  end
end

Drag options to blanks, or click blank then click option'

A:status

B:path

C>=

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using string keys instead of symbols for payload

Using equality (==) instead of greater-than-or-equal (>=) for status check

In Rails, the process_action.action_controller notification payload contains :status and :path keys, which can be used to monitor and log server errors (status ≥ 500).

Practice

1. What is the main purpose of logging in a Rails application?

easy

A. To record events and errors for later review

B. To monitor real-time server performance

C. To deploy the application automatically

D. To manage database migrations

Solution

1. Step 1: Understand logging purpose

   Logging captures events and errors that happen in the app so developers can check them later.

2. Step 2: Differentiate from monitoring

   Monitoring is about watching app health live, not storing past events.

3. Final Answer:

   To record events and errors for later review -> Option A

4. Quick Check:

   Logging = record events/errors [OK]

Hint: Logging saves past events; monitoring watches live [OK]

Common Mistakes:

• Confusing logging with monitoring
• Thinking logging deploys apps
• Mixing logging with database tasks

2. Which of the following is the correct way to write a log message in Rails?

easy

A. logger.write("User signed in")

B. Rails.log('info', 'User signed in')

C. log.info('User signed in')

D. Rails.logger.info "User signed in"

Solution

1. Step 1: Recall Rails logging syntax

   Rails uses Rails.logger with methods like info, error, debug to write logs.

2. Step 2: Check each option

   Only Rails.logger.info "User signed in" uses correct Rails.logger.info syntax.

3. Final Answer:

   Rails.logger.info "User signed in" -> Option D

4. Quick Check:

   Rails.logger.info is correct syntax [OK]

Hint: Use Rails.logger.method("message") for logging [OK]

Common Mistakes:

• Using undefined logger object
• Wrong method names like write or log
• Incorrect method call syntax

3. Given this Rails code snippet, what will be the log level of the message?

Rails.logger.warn "Disk space low"

medium

A. Info

B. Warn

C. Error

D. Debug

Solution

1. Step 1: Identify the logging method used

   The method called is warn, which sets the log level to warning.

2. Step 2: Match method to log level

   Rails.logger.warn writes a warning level message.

3. Final Answer:

   Warn -> Option B

4. Quick Check:

   Rails.logger.warn = Warn level [OK]

Hint: Method name matches log level (warn = Warn) [OK]

Common Mistakes:

• Confusing warn with info or error
• Assuming default log level is info
• Mixing debug and warn levels

4. You added this line in a Rails controller but no log appears:

logger.error "Payment failed"

What is the most likely reason?

medium

A. The log level is set higher than error

B. Rails.logger must be used instead of logger

C. The logger object is not defined in controllers

D. Logging is disabled by default in Rails

Solution

1. Step 1: Understand logger availability in controllers

   In Rails controllers, logger is available as a shortcut to Rails.logger.

2. Step 2: Check log level settings

   If the log level is set higher than error (like fatal), error messages won't show.

3. Final Answer:

   The log level is set higher than error -> Option A

4. Quick Check:

   Log level filters out lower severity logs [OK]

Hint: Check log level filters if logs don't appear [OK]

Common Mistakes:

• Assuming logger is undefined in controllers
• Thinking Rails.logger must be used always
• Believing logging is off by default

5. You want to monitor your Rails app's performance in production. Which approach is best?

hard

A. Use Rails built-in logger to track all performance metrics

B. Add custom puts statements in code to watch performance

C. Integrate an external monitoring tool like New Relic or Datadog

D. Rely on Rails console logs only

Solution

1. Step 1: Understand Rails logging limits

   Rails logging records events but does not provide detailed real-time performance monitoring.

2. Step 2: Identify best monitoring practice

   External tools like New Relic or Datadog specialize in monitoring app health and performance live.

3. Final Answer:

   Integrate an external monitoring tool like New Relic or Datadog -> Option C

4. Quick Check:

   Use external tools for monitoring, not just logs [OK]

Hint: Use specialized tools for monitoring, not just logs [OK]

Common Mistakes:

• Expecting Rails logger to monitor performance live
• Using puts for monitoring which is not scalable
• Ignoring external monitoring solutions