How do I initiate rolling updates on my Auto Scaling group when there are no changes to the launch template in CloudFormation?

Resolution

To initiate rolling updates for an Auto Scaling group, use the UpdatePolicy attribute.

In your CloudFormation template's launch configuration, it's a best practice to reference the Toggle parameter in the UserData property of your AWS::EC2::LaunchTemplate resource type. When you change the Toggle value, for example from true to false, during a stack update, you modify the UserData property. This action prompts CloudFormation to create a new launch template version.

The following resolution assumes that you configured the AutoScalingRollingUpdate policy for your Auto Scaling group, and you configured your Auto Scaling group to reference AWS::EC2::LaunchTemplate.

Important: Make sure that you don't disrupt other elements in the UserData property when you add the Toggle parameter to your template.

To set up rolling updates, complete the following steps:

1. In your CloudFormation template, define Toggle as a parameter.
   For a JSON file, enter the following code:

       "Parameters": {
           "Toggle": {
               "Type": "String",
               "AllowedValues": [
                   "true",
                   "false"
               ],
               "Default": "true",
               "Description": "Toggle parameter to force ASG update"
           }
       }

   For a YAML file, enter the following code:

   Parameters:
     Toggle:
       Type: String
       AllowedValues: 
         - 'true'
         - 'false'
       Default: 'true'
       Description: 'Toggle parameter to force ASG update'

2. In your template's launch configuration, reference the Toggle parameter in the UserData property.
   JSON example:

           "LaunchTemplate": {
               "Type": "AWS::EC2::LaunchTemplate",
               "Properties": {
                   "LaunchTemplateData": {
                       "ImageId": { "Ref": "ImageId" },
                       "UserData": {
                           "Fn::Base64": {
                               "Fn::Join": [
                                   "",
                                   [
                                       "#!/bin/bash\n",
                                       "echo \"Toggle parameter is set to ",
                                       {
                                           "Ref": "Toggle"
                                       },
                                       "\"\n"
                                       ...
                                       ...
                                   ]
                               ]
                           }
                       },
                       "InstanceType": { "Ref": "InstanceType" }
                   }
               }

   YAML example:

     LaunchTemplate:
       Type: AWS::EC2::LaunchTemplate
       Properties:
         LaunchTemplateData:
           ImageId: !Ref ImageId
           UserData:
             Fn::Base64:
               !Sub |
                 #!/bin/bash
                 echo "Toggle parameter is set to ${Toggle}"
                 ...
                 ...
           InstanceType: !Ref InstanceType

3. Create your stack.

4. To initiate rolling updates, change the value of the Toggle parameter from true to false or false to true, depending on its current setting.

Note: You can also use the preceding resolution on properties where an update requires a replacement, such as LaunchTemplateName.