Ruby on Rails Log Collection

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To send your logs to Datadog, log to a file with Lograge and tail this file with your Datadog Agent. When setting up logging with Ruby, keep in mind the reserved attributes.

Using Lograge, you can transform the standard text-based log format, like in this example:

Started GET "/" for at 2012-03-10 14:28:14 +0100
Processing by HomeController#index as HTML
  Rendered text template within layouts/application (0.0ms)
  Rendered layouts/_assets.html.erb (2.0ms)
  Rendered layouts/_top.html.erb (2.6ms)
  Rendered layouts/_about.html.erb (0.3ms)
  Rendered layouts/_google_analytics.html.erb (0.4ms)
Completed 200 OK in 79ms (Views: 78.8ms | ActiveRecord: 0.0ms)

To the following JSON format of the log, which provides more structure:

  "timestamp": "2016-01-12T19:15:19.118829+01:00",
  "level": "INFO",
  "logger": "Rails",
  "method": "GET",
  "path": "/jobs/833552.json",
  "format": "json",
  "controller": "jobs",
  "action": "show",
  "status": 200,
  "duration": 58.33,
  "view": 40.43,
  "db": 15.26

Install and configure your logger

  1. Add the lograge gem to your project:
    gem 'lograge'
  2. In your configuration file, set the following to configure Lograge:
    # Lograge config
    config.lograge.enabled = true
    # This specifies to log in JSON format
    config.lograge.formatter =
    ## Disables log coloration
    config.colorize_logging = false
    # Log to a dedicated file
    config.lograge.logger ='log', "#{Rails.env}.log"))
    # This is useful if you want to log query parameters
    config.lograge.custom_options = lambda do |event|
        { :ddsource => 'ruby',
          :params => event.payload[:params].reject { |k| %w(controller action).include? k }
    Note: Lograge can also add contextual information to your logs. See the Lograge documentation for more details.

For a more in-depth example of this setup, see How to collect, customize, and manage Rails application logs.


To configure Lograge for rocket_pants controllers, in the config/initializers/lograge_rocketpants.rb file (the location can vary depending on your project):

# Come from here:
app = Rails.application
if app.config.lograge.enabled
  ActiveSupport::LogSubscriber.log_subscribers.each do |subscriber|
    case subscriber
      when ActionController::LogSubscriber
        Lograge.unsubscribe(:rocket_pants, subscriber)
  Lograge::RequestLogSubscriber.attach_to :rocket_pants
  1. Add the grape_logging gem to your project:

    gem 'grape_logging'
  2. Add the additional configuration to Grape:

    use GrapeLogging::Middleware::RequestLogger,
          instrumentation_key: 'grape',
          include: [,
  3. Create the config/initializers/instrumentation.rb file and add the following configuration:

    # Subscribe to grape request and log with a logger dedicated to Grape
    grape_logger = Logging.logger['Grape']
    ActiveSupport::Notifications.subscribe('grape') do |name, starts, ends, notification_id, payload| payload

Configure the Datadog Agent

Once log collection is enabled, do the following to set up custom log collection to tail your log files and send them to Datadog.

  1. Create a ruby.d/ folder in the conf.d/ Agent configuration directory.
  2. Create a conf.yaml file in ruby.d/ with the following content:
        - type: file
          path: "<RUBY_LOG_FILE_PATH>.log"
          service: <SERVICE_NAME>
          source: ruby
          sourcecategory: sourcecode
          ## Uncomment the following processing rule for multiline logs if they
          ## start by the date with the format yyyy-mm-dd
          #  - type: multi_line
          #    name: new_log_start_with_date
          #    pattern: \d{4}\-(0?[1-9]|1[012])\-(0?[1-9]|[12][0-9]|3[01])
  3. Restart the Agent.
  4. Run the Agent’s status subcommand and look for ruby under the Checks section to confirm that logs are successfully submitted to Datadog.

If logs are in JSON format, Datadog automatically parses the log messages to extract log attributes. Use the Log Explorer to view and troubleshoot your logs.

Connect logs and traces

If APM is enabled for this application, you can improve the connection between application logs and traces by following the APM Ruby logging instructions to automatically add trace and span IDs in your logs.

Best practices

Add additional context (user, session, action, and metrics) to your logs when possible.

Instead of logging simple string messages, you can use log hashes as shown in the following example:

my_hash = {'user' => '1234', 'button_name'=>'save','message' => 'User 1234 clicked on button saved'};;

The hash is converted into JSON and you can carry out analytics for user and button_name:

  "timestamp": "2016-01-12T19:15:18.683575+01:00",
  "level": "INFO",
  "logger": "WelcomeController",
  "message": {
    "user": "1234",
    "button_name": "save",
    "message": "User 1234 clicked on button saved"

Further Reading