How do I update my EBS volume in CloudFormation even when I don't replace my EC2 instances?

Resolution

To prevent instance replacement, it's a best practice to use the AWS::EC2::Volume resource type when you update EBS volumes in CloudFormation.

Instance replacement occurs when you specify volumes in the BlockDeviceMappings property of the AWS::EC2::Instance and AWS::EC2::Template resource types. In this scenario, you must add a retain DeletionPolicy attribute.

Important: If you manually modify the volume, such as from gp2 to gp3, then you must also modify the volume that's attached to the instance. Verify that the instance isn't in the Optimizing or Modifying state. Before you modify the volume to gp3, make sure that you adhere to the volume modification requirements.

To avoid instance replacement when you modify volumes that you specify with the BlockDeviceMappings property, complete the following steps.

Add a retain DeletionPolicy attribute to the target AWS::EC2::Instance template resource

Complete the following steps:

1. Take a snapshot of the volumes to create a backup of critical workloads.

2. Set the DeletionPolicy to Retain in the CloudFormation stack of the instance with the volume that you want to update. Example:

   AWSTemplateFormatVersion: '2010-09-09'
   Resources:
    Myinstance:
     Type: AWS::EC2::Instance
     DeletionPolicy: Retain
     Properties:
      BlockDeviceMappings:
       - DeviceName: /dev/xvda
        Ebs:
         VolumeType: gp2
         VolumeSize: 10
         DeleteOnTermination: true
      EbsOptimized: false
      ImageId: ami-064ff912f78e3e561
      InstanceInitiatedShutdownBehavior: stop
      InstanceType: t2.micro
      Monitoring: false

3. Update the stack.

Remove the resource from its CloudFormation stack and implement your changes

Complete the following steps:

1. Remove the instance from the template to remove the instance from the CloudFormation stack but not delete the underlying resource. Then, manually modify the EC2 instance.
   Note: If you have only one resource in your template, then you must create a stand-in resource, such as another instance. You can delete the resource from the template after you import the EC2 instance back into the template.
2. Modify the EBS volume attributes.

Import the resource back into your CloudFormation stack

Complete the following steps:

1. Open the CloudFormation console.

2. In the navigation pane, choose Stack.

3. Choose Stack actions, and then choose Import resources into stack.

4. Enter the updated CloudFormation template. Example:

   AWSTemplateFormatVersion: '2010-09-09'
   Resources:
    Myinstance:
     Type: AWS::EC2::Instance
     DeletionPolicy: Retain
     Properties: 
      BlockDeviceMappings:
       - DeviceName: /dev/xvda
         Ebs:
          VolumeType: gp3 
          VolumeSize: 100
          DeleteOnTermination: true
       EbsOptimized: false
       ImageId: ami-064ff912f78e3e561
       InstanceInitiatedShutdownBehavior: stop
       InstanceType: t2.micro
       Monitoring: false

   Note: To import a resource, the CloudFormation template must describe the resource with its existing configurations.

5. For Identifier, enter the instance ID.

6. Choose Import resource.

After CloudFormation updates the status to IMPORT_COMPLETE, the instance is part of the stack.

You might receive the "There was an error creating this change set. As part of the import operation, you cannot modify or add [Outputs]" error message. To resolve this issue, verify that the Outputs section of the latest CloudFormation template matches the template that your stack uses. If they're not the same, then update the latest CloudFormation template to match the values in the Outputs section of the template that your stack uses. Then, update the stack again.