Datadog Environment Specific Configuration in Rails

Installing Datadog Agents

Datadog Agents collect logs, metrics, traces from the Rails application and forward it. The servers need to have this agent installed to forward the logs. Generate an API Key and run the following command being ubuntu user:

DD_API_KEY=<API_KEY> DD_AGENT_MAJOR_VERSION=7 bash -c "$(curl -L <https://raw.githubusercontent.com/DataDog/datadog-agent/master/cmd/agent/install_script.sh)">

Checking the status of datadog-agent:

sudo datadog-agent status

Starting/Restarting/Enabling/disabling datadog-agent:

sudo systemctl <status|restart|disable|enable> datadog-agent

Configure Agent to collect request logs and traces

Datadog agents APM and logs tracing is disabled by default. For all of the servers where datadog-agent is installed, copy the configuration file /etc/datadog-agent/datadog.yaml to /etc/datadog-agent/datadog.yaml.sample and edit datadog.yaml file.

api_key: <API_KEY>
site: datadoghq.com
env: <staging | production>
logs_enabled: true # this is for logs management, will need later
apm_config: 
  enabled: true
  env: <staging | production | test | pre-prod>

sudo systemctl restart datadog-agent

Rails Initializers Configuration

Datadog uses the ddtrace gem and a Rails initializer file for instrumenting your application. Add the following gem to your Gemfile:

gem 'ddtrace'

then bundle install:

bundle install

Next, create a datadog.rb file in your application’s config/initializers directory:

# config/initializers/datadog.rb
require 'ddtrace'

app_name = 'your-app-name'
configured_environments = %w(staging production preprod)
environment = ENV['RAILS_ENV']

if configured_environments.include?(environment)
  Datadog.configure do |c|
    c.tracer enabled: true
    c.env = environment

    # <https://github.com/DataDog/dd-trace-rb/blob/master/docs/GettingStarted.md#rails>
    c.use :rails,
        service_name: app_name + '-app',
        database_service: app_name + '-postgres',
        controller_service: app_name + '-controller',
        distributed_tracing: true,
        middleware_names: true

    c.use :sidekiq, client_service_name: "#{app_name}-app", service_name: "#{app_name}-sidekiq", tag_args: true

    # <https://github.com/DataDog/dd-trace-rb/blob/master/docs/GettingStarted.md#aws>
    c.use :aws, service_name: "#{app_name}-aws"
    c.use :redis, service_name: "#{app_name}-redis"

    # <https://github.com/DataDog/dd-trace-rb/blob/master/docs/GettingStarted.md#nethttp>
    c.use :http, split_by_domain: true
  end
else
  Datadog.configure do |c|
    c.tracer enabled: false
  end
end

c.env = environment is required to categorize/scope traces/logs based on the environment.

Sending Deployment Metrics to Datadog

There is a tag called version that is read by datadog to find out changes between codes and compare deployments. If you use Capistrano application uses capistrano for deployments and capistrano creates a file called REVISION in the remote folder. The file contains the latest commit hash git rev-parse HEAD which can be sent to datadog as a new version. Let’s write a module to extract that version and send it to datadog.

module Configuration
  module Version
    module_function

    REVISION_FILE_NAME = 'REVISION'

    # find latest commit hash from REVISION file inside current folder created by capistrano in servers
    def git_head
      File.read(Rails.root.join(REVISION_FILE_NAME)).strip
    end
  end
end

The method git_head can be called in datadog.rb like this.

...
  Datadog.configure do |c|
    ... 
    c.version = Configuration::Version.git_head
    ...
  end
...