Fargate上のRailsアプリを高速でオートスケールさせる

gem 'aws-sdk-cloudwatch'

# config/initializers/cloudwatch_puma_metrics.rb
require 'aws-sdk-cloudwatch'
require 'net/http'
require 'json'

CLOUDWATCH = Aws::CloudWatch::Client.new(region: 'ap-northeast-1')


Thread.new do
  loop do
    begin
      sleep 10
      Rails.logger.info("Sending Puma metrics to CloudWatch")
      uri = URI('http://127.0.0.1:9293/stats')
      res = Net::HTTP.start(uri.host, uri.port, open_timeout: 1, read_timeout: 1) do |http|
        http.get(uri.request_uri)
      end

      stats = JSON.parse(res.body)
      Rails.logger.info(stats.inspect)
      capacity = stats['pool_capacity']

      CLOUDWATCH.put_metric_data(
        namespace: 'Custom/Puma',
        metric_data: [
          {
            metric_name: 'ThreadPoolCapacity',
            value: capacity,
            unit: 'Count',
            storage_resolution: 1,
            dimensions: [
              { name: 'Cluster', value: ENV['ECS_CLUSTER'] || 'default' },
              { name: 'Service', value: ENV['ECS_SERVICE_NAME'] || 'rails' }
            ]
          }
        ]
      )
     
    rescue => e
      Rails.logger.error("CloudWatch Puma metric error: #{e.class}: #{e.message}")
    end
  end
end

class RequestCounter
  def initialize(app)
    @app = app
  end

  def call(env)
    REQUEST_COUNTER.increment
    @app.call(env)
  end
end

activate_control_app 'tcp://127.0.0.1:9293', { no_token: true }

aws configure

aws ecr get-login-password --region ap-northeast-1 | docker login --username AWS --password-stdin {AWSアカウントID}.dkr.ecr.ap-northeast-1.amazonaws.com

aws ecr create-repository \
        --repository-name rails \
        --image-scanning-configuration scanOnPush=true \
        --region ap-northeast-1

docker tag rails-demo:latest {AWSアカウントID}.dkr.ecr.ap-northeast-1.amazonaws.com/rails:latest

docker push {AWSアカウントID}.dkr.ecr.ap-northeast-1.amazonaws.com/rails:latest