feat: Adding EBS devices without overriding existing EBS mappings

[kennedy]

Description

• Add a new variable override_ebs_mapping (default: true)
• If override_ebs_mapping is false, it would create ebs_block_device resources external to the aws_instance and assigns it

Motivation and Context

By design, if ebs_block_device is defined in the aws_instance, Terraform will assume management over the full set of non-root EBS block devices for the instance, treating additional block devices as drift. With this PR, setting the variable override_ebs_mapping to false will allowing the user to create the ebs_block_device resources externally, leaving the pre-assigned/existing EBS device mapped in the AMI.

https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/instance#argument-reference

If you use ebs_block_device on an aws_instance, Terraform will assume management over the full set of non-root EBS block devices for the instance, and treats additional block devices as drift. For this reason, ebs_block_device cannot be mixed with external aws_ebs_volume + aws_ebs_volume_attachment resources for a given instance.

Resolves:

• 263

• 214

Relates to:

• https://github.com/hashicorp/terraform-provider-aws/issues/20305
• https://github.com/hashicorp/terraform-provider-aws/issues/21806

Breaking Changes

No breaking changes, the default value of override_ebs_mapping allows the module to behave as before.

There is an additional outputs, outputs.external_ebs_block_device

How Has This Been Tested?

• [x] I have tested and validated these changes using one or more of the provided examples/* projects

  I created a new example, examples\multi-ec2-with-external-attachment, with override_ebs_mapping set to false and assigned two additional EBS devices to each ec2 instance. I also ran examples\[complete,volume-attachment].

  
  Terraform v1.1.6
  on windows_amd64

• provider registry.terraform.io/hashicorp/aws v4.2.0

  
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