Auto Scaling group with no associated ELB

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Metadata

Id: cloudformation-aws-auto-scaling-group-with-no-associated-elb

Provider: AWS

Platform: CloudFormation

Severity: Medium

Category: Availability

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Description

Auto Scaling groups must be associated with a load balancer to distribute traffic and maintain availability during scaling and instance replacement. Without a load balancer, instances can become single points of failure and traffic may be routed unevenly.

In CloudFormation, the AWS::AutoScaling::AutoScalingGroup resource must define the LoadBalancerNames property, and it must be a non-empty list of Classic ELB names. Resources missing LoadBalancerNames or where LoadBalancerNames is an empty array will be flagged.

If your environment uses Application Load Balancers (ALBs) or Network Load Balancers (NLBs), attach the Auto Scaling group to target groups via the TargetGroupARNs property instead, since this rule only checks LoadBalancerNames.

Secure configuration example:

MyAutoScalingGroup:
  Type: AWS::AutoScaling::AutoScalingGroup
  Properties:
    LaunchConfigurationName: myLaunchConfig
    MinSize: '1'
    MaxSize: '3'
    LoadBalancerNames:
      - my-classic-elb

Compliant Code Examples

#this code is a correct code for which the query should not find any result
AWSTemplateFormatVersion: '2010-09-09'
Resources:
  myLaunchTemplate:
    Type: AWS::EC2::LaunchTemplate
    Properties:
      LaunchTemplateName: !Sub ${AWS::StackName}-launch-template
      LaunchTemplateData:
        BlockDeviceMappings:
          - Ebs:
              VolumeSize: 22
              VolumeType: gp2
              DeleteOnTermination: true
              Encrypted: true
            DeviceName: /dev/xvdcz
        CreditSpecification:
          CpuCredits: Unlimited
        ImageId: ami-02354e95b39ca8dec
        InstanceType: t2.micro
        KeyName: my-key-pair-useast1
        Monitoring:
          Enabled: true
        SecurityGroupIds:
          - sg-7c227019
          - sg-903004f8
  myASG:
    Type: AWS::AutoScaling::AutoScalingGroup
    Properties:
      AutoScalingGroupName: myASG
      MinSize: "1"
      MaxSize: "6"
      DesiredCapacity: "2"
      HealthCheckGracePeriod: 300
      LoadBalancerNames:
        - elb_1
        - elb_2
      LaunchTemplate:
        LaunchTemplateId: !Ref myLaunchTemplate
        Version: !GetAtt myLaunchTemplate.LatestVersionNumber
      VPCZoneIdentifier:
        - !Ref myPublicSubnet1
        - !Ref myPublicSubnet2
      MetricsCollection:
        - Granularity: "1Minute"
          Metrics:
            - "GroupMinSize"
            - "GroupMaxSize"
      Tags:
        - Key: Environment
          Value: Production
          PropagateAtLaunch: "true"
        - Key: Purpose
          Value: WebServerGroup
          PropagateAtLaunch: "false"

Non-Compliant Code Examples

#this is a problematic code where the query should report a result(s)
AWSTemplateFormatVersion: '2010-09-09'
Resources:
  myLaunchTemplate:
    Type: AWS::EC2::LaunchTemplate
    Properties:
      LaunchTemplateName: !Sub ${AWS::StackName}-launch-template
      LaunchTemplateData:
        BlockDeviceMappings:
          - Ebs:
              VolumeSize: 22
              VolumeType: gp2
              DeleteOnTermination: true
              Encrypted: true
            DeviceName: /dev/xvdcz
        CreditSpecification:
          CpuCredits: Unlimited
        ImageId: ami-02354e95b39ca8dec
        InstanceType: t2.micro
        KeyName: my-key-pair-useast1
        Monitoring:
          Enabled: true
        SecurityGroupIds:
          - sg-7c227019
          - sg-903004f8
  myASG:
    Type: AWS::AutoScaling::AutoScalingGroup
    Properties:
      AutoScalingGroupName: myASG
      MinSize: "1"
      MaxSize: "6"
      DesiredCapacity: "2"
      HealthCheckGracePeriod: 300
      LaunchTemplate:
        LaunchTemplateId: !Ref myLaunchTemplate
        Version: !GetAtt myLaunchTemplate.LatestVersionNumber
      VPCZoneIdentifier:
        - !Ref myPublicSubnet1
        - !Ref myPublicSubnet2
      MetricsCollection:
        - Granularity: "1Minute"
          Metrics:
            - "GroupMinSize"
            - "GroupMaxSize"
      Tags:
        - Key: Environment
          Value: Production
          PropagateAtLaunch: "true"
        - Key: Purpose
          Value: WebServerGroup
          PropagateAtLaunch: "false"
  myASG2:
    Type: AWS::AutoScaling::AutoScalingGroup
    Properties:
      AutoScalingGroupName: myASG2
      MinSize: "1"
      MaxSize: "6"
      DesiredCapacity: "2"
      HealthCheckGracePeriod: 300
      LoadBalancerNames: []
      LaunchTemplate:
        LaunchTemplateId: !Ref myLaunchTemplate
        Version: !GetAtt myLaunchTemplate.LatestVersionNumber
      VPCZoneIdentifier:
        - !Ref myPublicSubnet1
        - !Ref myPublicSubnet2
      MetricsCollection:
        - Granularity: "1Minute"
          Metrics:
            - "GroupMinSize"
            - "GroupMaxSize"
      Tags:
        - Key: Environment
          Value: Production
          PropagateAtLaunch: "true"
        - Key: Purpose
          Value: WebServerGroup
          PropagateAtLaunch: "false"
  myASG3:
    Type: AWS::AutoScaling::AutoScalingGroup
    Properties:
      AutoScalingGroupName: myASG
      MinSize: "1"
      MaxSize: "6"
      DesiredCapacity: "2"
      HealthCheckGracePeriod: 300
      LoadBalancerNames: []
      LaunchTemplate:
        LaunchTemplateId: !Ref myLaunchTemplate
        Version: !GetAtt myLaunchTemplate.LatestVersionNumber
      VPCZoneIdentifier:
        - !Ref myPublicSubnet1
        - !Ref myPublicSubnet2
      MetricsCollection:
        - Granularity: "1Minute"
          Metrics:
            - "GroupMinSize"
            - "GroupMaxSize"
      Tags:
        - Key: Environment
          Value: Production
          PropagateAtLaunch: "true"
        - Key: Purpose
          Value: WebServerGroup
          PropagateAtLaunch: "false"