get-ASAutoscalingGroup cannot return the correct Launch Template information when Mixed Instance type is enabled

[yuyangwu0325]

This is a :question: general question document

[yuyangwu0325]

When using AWS PowerShell Tool to get the information about the Auto Scaling group. However, this is not working for them and the Launch Template is shown as null.

I replicate this issue and found this is caused by Auto Scaling group has Mix Instance Type option enabled. Based on my test, if Auto Scaling group does not override the instance type provided by the ASG, the tool will work as expected:

PS C:\Users\Administrator> (Get-ASAutoScalingGroup -AutoScalingGroupName TestASG).LaunchTemplate

LaunchTemplateId LaunchTemplateName Version

---

lt-08b7c95168857c3c8 BestLT $Latest

However, as long as you enable this option, the command will fail:

PS C:\Users\Administrator> (Get-ASAutoScalingGroup -AutoScalingGroupName TestASG).LaunchTemplate PS C:\Users\Administrator>

This is caused by Launch Template info is return under MixedInstancesPolicy property when MIG is used in Auto Scaling group. Therefore, using the following command can return the correct info: (Get-ASAutoScalingGroup -AutoScalingGroupName test-autoscaling-group).MixedInstancesPolicy.LaunchTemplate.LaunchTemplateSpecification

This can be quite confusing. Hence we would like to suggest you to update the public doc: https://docs.aws.amazon.com/powershell/latest/reference/items/Get-ASAutoScalingGroup.html

[ashishdhingra]

Based on my review of the code for PowerShell CmdLet Get-ASAutoscalingGroup, it is just invoking the DescribeAutoScalingGroups on the service.

I observed the following using AWS CLI command aws autoscaling describe-auto-scaling-groups --auto-scaling-group-name test-autoscaling-group:

• When I didn't enable Combine purchase options and instance types option, CLI gave the following output:

{
    "AutoScalingGroups": [
        {
            "AutoScalingGroupName": "test-autoscaling-group",
            "AutoScalingGroupARN": "arn:aws:autoscaling:us-east-2:139480602983:autoScalingGroup:08474ae9-dc8c-4ad4-829b-d7d9a6edaead:autoScalingGroupName/test-autoscaling-group",
            "LaunchTemplate": {
                "LaunchTemplateId": "lt-06095fd619cb40371",
                "LaunchTemplateName": "test-launch-template",
                "Version": "$Default"
            },
            "MinSize": 1,
            "MaxSize": 1,
            "DesiredCapacity": 1,
            "DefaultCooldown": 300,
            "AvailabilityZones": [
                "us-east-2b"
            ],
            "LoadBalancerNames": [],
            "TargetGroupARNs": [],
            "HealthCheckType": "EC2",
            "HealthCheckGracePeriod": 300,
            "Instances": [
                {
                    "InstanceId": "i-0653cb2eaef0102b8",
                    "InstanceType": "t2.micro",
                    "AvailabilityZone": "us-east-2b",
                    "LifecycleState": "InService",
                    "HealthStatus": "Healthy",
                    "LaunchTemplate": {
                        "LaunchTemplateId": "lt-06095fd619cb40371",
                        "LaunchTemplateName": "test-launch-template",
                        "Version": "1"
                    },
                    "ProtectedFromScaleIn": false
                }
            ],
            "CreatedTime": "2021-03-29T21:19:22.108000+00:00",
            "SuspendedProcesses": [],
            "VPCZoneIdentifier": "subnet-0e554b79afc8e48ed",
            "EnabledMetrics": [],
            "Tags": [],
            "TerminationPolicies": [
                "Default"
            ],
            "NewInstancesProtectedFromScaleIn": false,
            "ServiceLinkedRoleARN": "arn:aws:iam::139480602983:role/aws-service-role/autoscaling.amazonaws.com/AWSServiceRoleForAutoScaling"
        }
    ]
}

Notice the LaunchTemplate property at the ASG object level.

 

• Then I enabled Combine purchase options and instance types option, CLI gave the following output:

  {
  "AutoScalingGroups": [
      {
          "AutoScalingGroupName": "test-autoscaling-group",
          "AutoScalingGroupARN": "arn:aws:autoscaling:us-east-2:139480602983:autoScalingGroup:08474ae9-dc8c-4ad4-829b-d7d9a6edaead:autoScalingGroupName/test-autoscaling-group",
          "MixedInstancesPolicy": {
              "LaunchTemplate": {
                  "LaunchTemplateSpecification": {
                      "LaunchTemplateId": "lt-06095fd619cb40371",
                      "LaunchTemplateName": "test-launch-template",
                      "Version": "$Default"
                  },
                  "Overrides": [
                      {
                          "InstanceType": "t2.micro"
                      },
                      {
                          "InstanceType": "t2.small"
                      }
                  ]
              },
              "InstancesDistribution": {
                  "OnDemandAllocationStrategy": "prioritized",
                  "OnDemandBaseCapacity": 0,
                  "OnDemandPercentageAboveBaseCapacity": 70,
                  "SpotAllocationStrategy": "capacity-optimized"
              }
          },
          "MinSize": 1,
          "MaxSize": 1,
          "DesiredCapacity": 1,
          "DefaultCooldown": 300,
          "AvailabilityZones": [
              "us-east-2b"
          ],
          "LoadBalancerNames": [],
          "TargetGroupARNs": [],
          "HealthCheckType": "EC2",
          "HealthCheckGracePeriod": 300,
          "Instances": [
              {
                  "InstanceId": "i-0653cb2eaef0102b8",
                  "InstanceType": "t2.micro",
                  "AvailabilityZone": "us-east-2b",
                  "LifecycleState": "InService",
                  "HealthStatus": "Healthy",
                  "LaunchTemplate": {
                      "LaunchTemplateId": "lt-06095fd619cb40371",
                      "LaunchTemplateName": "test-launch-template",
                      "Version": "1"
                  },
                  "ProtectedFromScaleIn": false
              }
          ],
          "CreatedTime": "2021-03-29T21:19:22.108000+00:00",
          "SuspendedProcesses": [],
          "VPCZoneIdentifier": "subnet-0e554b79afc8e48ed",
          "EnabledMetrics": [],
          "Tags": [],
          "TerminationPolicies": [
              "Default"
          ],
          "NewInstancesProtectedFromScaleIn": false,
          "ServiceLinkedRoleARN": "arn:aws:iam::139480602983:role/aws-service-role/autoscaling.amazonaws.com/AWSServiceRoleForAutoScaling",
          "CapacityRebalance": true
      }
  ]
  }

  Notice now that there is no LaunchTemplate property it ASG object level. Instead it returned MixedInstancesPolicy property at ASG object level, which has LaunchTemplate child property.  

On the similar lines, if you now examine the value of (Get-ASAutoScalingGroup -AutoScalingGroupName test-autoscaling-group).MixedInstancesPolicy, it returns the following:

InstancesDistribution                          LaunchTemplate
---------------------                          --------------
Amazon.AutoScaling.Model.InstancesDistribution Amazon.AutoScaling.Model.LaunchTemplate

So the value of (Get-ASAutoScalingGroup -AutoScalingGroupName test-autoscaling-group).LaunchTemplate is correctly returned as null based on observation from AWS CLI output and this is not a bug.

To get the value of LaunchTemplate, use the following command (Get-ASAutoScalingGroup -AutoScalingGroupName test-autoscaling-group).MixedInstancesPolicy.LaunchTemplate.LaunchTemplateSpecification.

[ashishdhingra]

Refer https://github.com/aws/aws-sdk-net/blob/master/sdk/src/Services/AutoScaling/Generated/Model/AutoScalingGroup.cs. There are separate LaunchTemplate and MixedInstancesPolicy properties.

MixInstancesPolicy class is here https://github.com/aws/aws-sdk-net/blob/master/sdk/src/Services/AutoScaling/Generated/Model/MixedInstancesPolicy.cs

Hence the PowerShell CmdLet's behavior is correct.

I think documentation update is the best way going forward.

[ashishdhingra]

We can add an example showing differences between mix instance type and normal scneario.

[ashishdhingra]

Example added