Logging and monitoring in Ruby on Rails

Introduction

Logging helps you keep track of what your app is doing. Monitoring watches your app's health and alerts you if something goes wrong.

You want to see errors happening in your Rails app.

You need to check how long requests take to process.

You want to know if your app is running smoothly over time.

You want to get alerts if the app crashes or slows down.

You want to keep records for debugging or audits.

Syntax

Ruby on Rails

Rails.logger.level = Logger::INFO
Rails.logger.info "Your message here"
Rails.logger.error "Error message here"

Rails.logger is the built-in logger in Rails apps.

You can set the log level to control what messages are saved (DEBUG, INFO, WARN, ERROR, FATAL).

Examples

Different log levels show different importance of messages.

Ruby on Rails

Rails.logger.debug "Debugging info"
Rails.logger.info "App started"
Rails.logger.warn "This might be a problem"
Rails.logger.error "Something went wrong"

Setting log level to ERROR means only error messages are saved.

Ruby on Rails

Rails.logger.level = Logger::ERROR
Rails.logger.info "This will NOT be logged"
Rails.logger.error "This will be logged"

In config/environments/development.rb, you can set logger output and level.

Ruby on Rails

config.logger = Logger.new(STDOUT)
config.log_level = :debug

Sample Program

This sets the log level to info and prints logs to the console. Then it logs an info and an error message.

Ruby on Rails

# config/environments/development.rb
Rails.application.configure do
  config.log_level = :info
  config.logger = Logger.new(STDOUT)
end

# In any controller or model
Rails.logger.info "User signed in"
Rails.logger.error "Failed to save record"

Important Notes

Logs usually include timestamps and severity levels automatically.

Monitoring tools like New Relic or Datadog can collect and show logs and app health.

Keep log files from growing too large by rotating them regularly.

Summary

Logging records app events and errors for later review.

Monitoring watches app health and alerts you to problems.

Rails has built-in logging you can configure easily.