EC2 Auto Scalingの新機能「reservations-then-balanced」でキャパシティ予約優先のAZ分散を試してみた

AWSTemplateFormatVersion: "2010-09-09"
Description: >
  ASG with reservations-then-balanced strategy.
  t4g.nano instances with ODCR priority in AZ-a, then balanced across AZs.

Parameters:
  CapacityReservationId:
    Type: String
    Description: "ODCR ID (e.g., cr-0123456789abcdef0) created by create-odcr.sh"

  SubnetAZa:
    Type: AWS::EC2::Subnet::Id
    Description: "Subnet in ap-northeast-1a"

  SubnetAZb:
    Type: AWS::EC2::Subnet::Id
    Description: "Subnet in ap-northeast-1c"

  SubnetAZc:
    Type: AWS::EC2::Subnet::Id
    Description: "Subnet in ap-northeast-1d"

  AmiId:
    Type: AWS::SSM::Parameter::Value<AWS::EC2::Image::Id>
    Default: /aws/service/ami-amazon-linux-latest/al2023-ami-kernel-default-arm64
    Description: "AMI ID (default: latest Amazon Linux 2023 ARM64)"

  DesiredCapacity:
    Type: Number
    Default: 3

  MinSize:
    Type: Number
    Default: 0

  MaxSize:
    Type: Number
    Default: 5

Resources:
  LaunchTemplate:
    Type: AWS::EC2::LaunchTemplate
    Properties:
      LaunchTemplateName: !Sub "${AWS::StackName}-lt"
      LaunchTemplateData:
        ImageId: !Ref AmiId
        InstanceType: t4g.nano
        TagSpecifications:
          - ResourceType: instance
            Tags:
              - Key: Name
                Value: !Sub "${AWS::StackName}-instance"

  AutoScalingGroup:
    Type: AWS::AutoScaling::AutoScalingGroup
    Properties:
      AutoScalingGroupName: !Sub "${AWS::StackName}-asg"
      LaunchTemplate:
        LaunchTemplateId: !Ref LaunchTemplate
        Version: !GetAtt LaunchTemplate.LatestVersionNumber
      VPCZoneIdentifier:
        - !Ref SubnetAZa
        - !Ref SubnetAZb
        - !Ref SubnetAZc
      MinSize: !Ref MinSize
      MaxSize: !Ref MaxSize
      DesiredCapacity: !Ref DesiredCapacity
      AvailabilityZoneDistribution:
        CapacityDistributionStrategy: balanced-best-effort
      CapacityReservationSpecification:
        CapacityReservationPreference: capacity-reservations-first
        CapacityReservationTarget:
          CapacityReservationIds:
            - !Ref CapacityReservationId