Migrate Amazon CloudFormation stacks to launch templates

To find Auto Scaling groups that use a launch configuration

• Use the following describe-auto-scaling-groups command to list the names of Auto Scaling groups that are using launch configurations in the specified Region. Include the --filters option to narrow the results to groups associated with a CloudFormation stack (by filtering by the aws:cloudformation:stack-name tag key).

  aws autoscaling describe-auto-scaling-groups --region REGION \
    --filters Name=tag-key,Values=aws:cloudformation:stack-name \
    --query 'AutoScalingGroups[?LaunchConfigurationName!=`null`].AutoScalingGroupName'

  The following shows example output.

  [
      "{stack-name}-group-1",
      "{stack-name}-group-2",
      "{stack-name}-group-3"
  ]

  You can find additional useful Amazon CLI commands for finding Auto Scaling groups to migrate and filtering the output in Migrate your Auto Scaling groups to launch templates.

To modify the stack template and update the stack

1. Follow the same general procedures for modifying the stack template described in Modifying a stack template in the Amazon CloudFormation User Guide.

2. Rewrite the launch configuration as a launch template. See the following example:

   Example: A simple launch configuration

   ---
   Resources:
     myLaunchConfig: 
       Type: AWS::AutoScaling::LaunchConfiguration
       Properties: 
         ImageId: ami-02354e95b3example
         InstanceType: t3.micro
         SecurityGroups:
           - !Ref EC2SecurityGroup
         KeyName: MyKeyPair
         BlockDeviceMappings: 
           - DeviceName: /dev/xvda
             Ebs: 
               VolumeSize: 150
               DeleteOnTermination: true
         UserData: 
           Fn::Base64: !Sub |
             #!/bin/bash -xe
             yum install -y aws-cfn-bootstrap
             /opt/aws/bin/cfn-signal -e $? --stack ${AWS::StackName} --resource myASG --region ${AWS::Region}

   Example: The launch template equivalent

   ---
   Resources:
     myLaunchTemplate:
       Type: AWS::EC2::LaunchTemplate
       Properties:
         LaunchTemplateName: !Sub ${AWS::StackName}-launch-template
         LaunchTemplateData:
           ImageId: ami-02354e95b3example
           InstanceType: t3.micro
           SecurityGroupIds:
             - Ref! EC2SecurityGroup
           KeyName: MyKeyPair
           BlockDeviceMappings: 
             - DeviceName: /dev/xvda
               Ebs: 
                 VolumeSize: 150
                 DeleteOnTermination: true
           UserData: 
             Fn::Base64: !Sub |
               #!/bin/bash -x
               yum install -y aws-cfn-bootstrap
               /opt/aws/bin/cfn-signal -e $? --stack ${AWS::StackName} --resource myASG --region ${AWS::Region}

   For reference information for all the properties that Amazon EC2 supports, see AWS::EC2::LaunchTemplate in the Amazon CloudFormation User Guide.

   Note how the launch template includes the LaunchTemplateName property with a value of !Sub ${AWS::StackName}-launch-template. This is required if you want the name of the launch template to include the stack name.

3. If the IamInstanceProfile property is present in your launch configuration, you must convert it to a structure and specify either the name or the ARN of the instance profile. For an example, see AWS::EC2::LaunchTemplate.

4. If the AssociatePublicIpAddress, InstanceMonitoring, or PlacementTenancy properties are present in your launch configuration, you must convert these to a structure. For examples, see AWS::EC2::LaunchTemplate.

   An exception is when the value for the MapPublicIpOnLaunch property on the subnets you used for your Auto Scaling group matches the value for the AssociatePublicIpAddress property in your launch configuration. In this case, you can ignore the AssociatePublicIpAddress property. The AssociatePublicIpAddress property is only used to override the MapPublicIpOnLaunch property to change whether instances receive a public IPv4 address at launch.

5. You can copy security groups from the SecurityGroups property to one of two places in your launch template. Normally, you copy the security groups to the SecurityGroupIds property. However, if you create a NetworkInterfaces structure within your launch template to specify the AssociatePublicIpAddress property, then you must copy the security groups to the Groups property of the network interface instead.

6. If any BlockDeviceMapping structures are present in your launch configuration with NoDevice set to true, then you must specify an empty string for NoDevice in your launch template to have Amazon EC2 omit the device.

7. If the SpotPrice property is present in your launch configuration, we recommend that you omit it from your launch template. Your Spot Instances will launch at the current Spot price. This price will never exceed the On-Demand price.

   To request Spot Instances, you have two mutually exclusive options:

   • The first is to use the InstanceMarketOptions structure in your launch template (not recommended). For more information, see AWS::EC2::LaunchTemplate InstanceMarketOptions in the Amazon CloudFormation User Guide.

   • The other is to add a MixedInstancesPolicy structure to your Auto Scaling group. Doing so provides you with more options for how you make the request. A Spot Instance request in your launch template doesn't support more than one instance type selection per Auto Scaling group. However, a mixed instances policy does support more than one instance type selection per Auto Scaling group. Spot Instance requests benefit from having more than one instance type to choose from. For more information, see AWS::AutoScaling::AutoScalingGroup MixedInstancesPolicy in the Amazon CloudFormation User Guide.

8. Remove the LaunchConfigurationName property from the AWS::AutoScaling::AutoScalingGroup resource. Add the launch template in its place.

   In the following examples, the Ref intrinsic function gets the ID of the AWS::EC2::LaunchTemplate resource with the logical ID myLaunchTemplate. The GetAtt function gets the latest version number (for example, 1) of the launch template for the Version property.

   Example: Without a mixed instances policy

   ---
   Resources:
     myASG:
       Type: AWS::AutoScaling::AutoScalingGroup
       Properties:
         LaunchTemplate:
           LaunchTemplateId: !Ref myLaunchTemplate
           Version: !GetAtt myLaunchTemplate.LatestVersionNumber
         ...

   Example: With a mixed instances policy

   ---
   Resources:
     myASG:
       Type: AWS::AutoScaling::AutoScalingGroup
       Properties:        
         MixedInstancesPolicy:
           LaunchTemplate:
             LaunchTemplateSpecification:
               LaunchTemplateId: !Ref myLaunchTemplate
               Version: !GetAtt myLaunchTemplate.LatestVersionNumber
         ...

   For reference information for all the properties that Amazon EC2 Auto Scaling supports, see AWS::AutoScaling::AutoScalingGroup in the Amazon CloudFormation User Guide.

9. When you are ready to deploy these updates, follow the CloudFormation procedures to update the stack with your modified stack template. For more information, see Modifying a stack template in the Amazon CloudFormation User Guide.

To track the migration

1. In the Amazon CloudFormation console, select the stack that you updated and then choose the Events tab to view the stacks events.

2. To update the event list with the most recent events, choose the refresh button in the CloudFormation console.

3. While your stack is updating, you will notice multiple events for each resource update. If you see an exception in the Status reason column that indicates a problem when trying to create the launch template, see Troubleshoot Amazon EC2 Auto Scaling: Launch templates for potential causes.

4. (Optional) Depending on your use of the UpdatePolicy attribute, you can monitor the progress of your Auto Scaling group from the Auto Scaling groups page of the Amazon EC2 console. Select the Auto Scaling group. On the Activity tab, under Activity history, the Status column shows whether your Auto Scaling group has successfully launched or terminated instances, or whether the scaling activity is still in progress.

5. When the stack update is complete, CloudFormation issues an UPDATE_COMPLETE stack event. For more information, see Monitoring the progress of a stack update in the Amazon CloudFormation User Guide.

6. After the stack update is complete, open the Launch templates page and Launch configurations page of the Amazon EC2 console. You will notice a new launch template is created, and the launch configuration is deleted.