Checks the status and AMI ID of instances in the ASG of a CloudFormation stack (used to test an AMI rotation script)

cf_asg_instances_status_check.rb

#!/usr/bin/env ruby

require 'aws-sdk'
require 'forwardable'

DEFAULT_REGION = "us-east-1".freeze
STACK_NAMES = ['market-dj'].freeze

class Instance
  extend Forwardable
  delegate [:image_id] => :ec2_instance_resource
  delegate [:health_status, :lifecycle_state] => :as_instance_resource
  attr_reader :instance_id

  def initialize(instance_id, client_options = { region: DEFAULT_REGION }, ec2_instance_resource: nil, as_instance_resource: nil)
    @instance_id, @client_options = instance_id, client_options
    @ec2_instance_resource, @as_instance_resource = ec2_instance_resource, as_instance_resource
  end

  private

  def ec2_instance_resource
    @ec2_instance_resource ||= ec2_client.describe_instances(instance_ids: [@instance_id]).reservations.first.instances.first
  end

  def as_instance_resource
    @as_instance_resource ||= ec2_client.describe_instances(instance_ids: [@instance_id]).reservations.first.instances.first
  end

  def ec2_client
    @ec2_client ||= Aws::EC2::Client.new(@client_options)
  end

  def as_client
    @as_client ||= Aws::AutoScaling::Client.new(@client_options)
  end
end

class Asg
  def initialize(asg_name, client_options = { region: DEFAULT_REGION })
    @asg_name, @client_options = asg_name, client_options
  end

  def latest_ami_id
    @latest_ami_id ||= as_launch_config_resouce.image_id
  end

  def instances
    as_instance_resources = as_asg_resource.instances.group_by(&:instance_id)
    ec2_instance_resources = ec2_client.describe_instances(instance_ids: as_instance_resources.keys).reservations.flat_map(&:instances).group_by(&:instance_id)
    as_instance_resources.map do |instance_id, as_instance_resources|
      as_instance_resource = as_instance_resources.first
      ec2_instance_resource = ec2_instance_resources[instance_id].first
      # Passing the resources directly to the Instance allows us to make only 2 queries
      # (one on the autoscaling client and one on the EC2 client) for all the instances
      # rather than 2 queries for each instance
      Instance.new(instance_id, @client_options, as_instance_resource: as_instance_resource, ec2_instance_resource: ec2_instance_resource)
    end
  end

  def instance_statuses
    instances.map do |i|
      { :id => i.instance_id, :health => i.health_status, :state => i.lifecycle_state, :ami => i.image_id }
    end
  end

  private

  def as_asg_resource
    as_client.describe_auto_scaling_groups(auto_scaling_group_names: [@asg_name]).auto_scaling_groups.first
  end

  def as_launch_config_resource
    as_client.describe_launch_configurations(launch_configuration_names: [as_asg_resource.launch_configuration_name]).launch_configurations.first
  end

  def as_client
    @as_client ||= Aws::AutoScaling::Client.new(@client_options)
  end

  def ec2_client
    @ec2_client ||= Aws::EC2::Client.new(@client_options)
  end
end

class Stack
  def initialize(stack_name, client_options = { region: DEFAULT_REGION })
    @stack_name, @client_options = stack_name, client_options
  end

  def asg
    @asg ||= Asg.new(asg_name, @client_options)
  end

  private

  def asg_name
    cf_asg_resource.physical_resource_id
  end

  def cf_asg_resource
    @cf_asg_summary ||= cf_client.describe_stack_resources(stack_name: @stack_name, logical_resource_id: 'AutoScalingGroup').stack_resources.first
  end

  def cf_client
    @cf_client ||= ::Aws::CloudFormation::Client.new(@client_options)
  end
end

last_state = nil
while true do
  new_state = Stack.new('market-dj').asg.instance_statuses
  if new_state != last_state
    p Time.now
    new_state.each do |i|
      print "#{i[:id]} #{i[:ami]} #{i[:state]} #{i[:health]}\n"
    end
    last_state = new_state
  end
  sleep 0.1
end