Script to add custom tag groups to all StatsD-reported Datadog metrics. Don't run it unless you understand what it does. Tags in `TAGS_TO_EXCLUDE` are excluded from the custom tag groups.

add_custom_tag_groups.rb

# frozen_string_literal: true

require 'datadog_api_client'
require 'json'

class AddCustomTagGroups
  ALL_METRICS_FILE = "metrics.txt"
  METRIC_TYPES_FILE = "metric_types.json"
  METRIC_TAGS_FILE = "metric_tags.json"
  TAGS_TO_EXCLUDE = [
    # Put the names of tags you want to exclude here! Otherwise this script won't be useful.
  ]

  def call
    statsd_metric_types.each_key.with_index do |metric, i|
      puts "#{metric} #{i} of #{statsd_metric_types.size}"
      tags_for_metric = metric_tags[metric]
      if tags_for_metric.nil? || tags_for_metric.empty?
        puts "no tags for metric #{metric.inspect}"
        next
      end
      tags_to_keep = tags_for_metric.to_a - TAGS_TO_EXCLUDE
      body = DatadogAPIClient::V2::MetricTagConfigurationCreateRequest.new(
        {
          data: DatadogAPIClient::V2::MetricTagConfigurationCreateData.new(
            {
              id: metric,
              type: DatadogAPIClient::V2::MetricTagConfigurationType::MANAGE_TAGS,
              attributes: {
                tags: tags_to_keep,
                metric_type: statsd_metric_types.fetch(metric).fetch("type")
              },
            }
          )
        }
      )
      attempts = 0
      begin
        attempts += 1
        # Create a tag configuration
        result = api_instance_v2.create_tag_configuration(metric, body)
        p result
      rescue DatadogAPIClient::V2::APIError => e
        puts "Error when calling MetricsAPI->create_tag_configuration: #{e}"
        if e.code == 429 && attempts < 3
          puts "rate-limited; retrying"
          sleep 60
          retry
        end
      end
      sleep 1
    end
  end

  def metric_tags
    return @metric_tags if defined?(@metric_tags)

    unless File.exist?(METRIC_TAGS_FILE)
      metric_tags = statsd_metric_types.each_key.with_index.with_object({}) do |(metric, i), metric_tags|
        puts "#{i} of #{statsd_metric_types.size}"
        sleep 60.fdiv(50) + 0.1
        response = api_instance_v2.list_tags_by_metric_name(metric)
        tags = response.data.attributes.tags
        tag_keys = tags.each_with_object(Set.new) { |tag, set| set << tag.split(":")[0] }
        metric_tags[metric] = tag_keys.to_a
      rescue DatadogAPIClient::V2::APIError
        puts "error, retrying"
        sleep 60
        retry
      end

      File.write(METRIC_TAGS_FILE, JSON.pretty_generate(metric_tags))
    end
    @metric_tags = JSON.parse(File.read(METRIC_TAGS_FILE))
  end

  def all_metrics
    return @all_metrics if defined?(@all_metrics)

    unless File.exist?(ALL_METRICS_FILE)
      from = Integer(Time.now - 3600 * 24) # 1 day ago
      response = api_instance.list_active_metrics(from)
      metrics = response.metrics
      File.open(ALL_METRICS_FILE, "w") do |file|
        metrics.each do |metric|
          file.puts(metric)
        end
      end
    end

    @all_metrics = File.readlines(ALL_METRICS_FILE, chomp: true)
  end

  def metric_types
    return @metric_types if defined?(@metric_types)

    unless File.exist?(METRIC_TYPES_FILE)
      metric_types = {}

      all_metrics.each_with_index do |metric, i|
        response = api_instance.get_metric_metadata(metric)
        metric_types[metric] = response.to_hash
      end

      File.write(METRIC_TYPES_FILE, JSON.pretty_generate(metric_types))
    end
    @metric_types = JSON.parse(File.read(METRIC_TYPES_FILE))
  end

  def api_instance
    @api_instance ||= DatadogAPIClient::V1::MetricsAPI.new
  end

  def api_instance_v2
    return @api_instance_v2 if defined?(@api_instance_v2)

    DatadogAPIClient::V2.configure do |config|
      config.unstable_operations[:create_tag_configuration] = true
      config.unstable_operations[:list_tag_configuration_by_name] = true
    end
    @api_instance_v2 = DatadogAPIClient::V2::MetricsAPI.new
  end

  def statsd_metric_types
    @statsd_metric_types ||= metric_types.select do |name, attrs|
      attrs.key?("statsd_interval")
    end
  end
end

AddCustomTagGroups.new.call