Ruby on Rails log collection

To send your logs to Datadog, it’s recommend to log to a file with lograge and then tail this file with your Datadog Agent. When setting up logging with Ruby, make sure to keep in mind the reserved attributes.

Instead of having a Rail logging output like this:

Started GET "/" for 127.0.0.1 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)

After lograge formating you get a single log line with all the important information in a JSON format like this:

{
  "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
}

Setup

This section describe the minimum setup required in order to forward your Rails application logs to Datadog, if you want a more in depth example of this setup refer to the blog article: How to collect, customize, and manage Rails application logs.

Add the lograge GEM in your project:
```
gem 'lograge'
```

Configure Lograge. In your configuration file, set the following:

# Lograge config
config.lograge.enabled = true

# This specifies to log in JSON format
config.lograge.formatter = Lograge::Formatters::Json.new

## Disables log coloration
config.colorize_logging = false

# Log to a dedicated file
config.lograge.logger = ActiveSupport::Logger.new(File.join(Rails.root, '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 }
    }
end

Note: You can also ask Lograge to add contextual information to your logs. Refer to the official doc if you are interested: Lograge documentation

Configure your Datadog Agent. Create a ruby.d/conf.yaml file in your conf.d/ folder with the following content:

  logs:
    - type: file
      path: "<RUBY_LOG_FILE_PATH>.log"
      service: ruby
      source: ruby
      sourcecategory: sourcecode
      ## Uncomment the following processing rule for multiline logs if they
      ## start by the date with the format yyyy-mm-dd
      #log_processing_rules:
      #  - 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])

Learn more about the Agent log collection.

Restart the Agent

Getting further

Connect logs and traces

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

Good logging practices in your application

Now that your logging configuration is sending proper JSON, you should exploit it as much as you can.

A logging practice is to bring as much context (user, session, action, metrics, etc…) to every line of log you send. To do so you can actually instead of logging simple string messages you should log hashes as shown in the following example:

my_hash = {'user' => '1234', 'button_name'=>'save','message' => 'User 1234 clicked on button saved'};
logger.info(my_hash);

The hash is going to get converted into JSON and you’ll then be able to do analytics over 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"
  }
}

RocketPants suggested logging configuration

In the file config/initializers/lograge_rocketpants.rb (it can change depending on your project):

# Configure Lograge to work with rocket_pants' controllers
#
# Come from here:
#   https://github.com/Sutto/rocket_pants/issues/111
#
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)
    end
  end
  Lograge::RequestLogSubscriber.attach_to :rocket_pants
end

Grape’s suggested logging configuration

Add the grape_logging gem:

gem 'grape_logging'

Pass additional configuration to Grape:

use GrapeLogging::Middleware::RequestLogger,
      instrumentation_key: 'grape',
      include: [ GrapeLogging::Loggers::Response.new,
                 GrapeLogging::Loggers::FilterParameters.new ]

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|
    grape_logger.info payload
end