[Bug]: ReservationCapacityExceeded error when changing capacity reservation id and instance_type of aws_instance

[atikhono]

Terraform Core Version

1.5.2

AWS Provider Version

5.7.0

Affected Resource(s)

• aws_instance

Expected Behavior

Instance should have new instance_type and capacity reservation ID

Actual Behavior

Instance was stopped, instance_type updated, then instance failed to start because of reservation capacity type and instance type mismatch.

I can see that instance type update is not linked to capacity reservation change, and happens earlier:
https://github.com/hashicorp/terraform-provider-aws/blob/v5.7.0/internal/service/ec2/ec2_instance.go#L1662
https://github.com/hashicorp/terraform-provider-aws/blob/v5.7.0/internal/service/ec2/ec2_instance.go#L1936
That explains the behaviour. I suppose when aws_instance has instance_type and capacity reservation ID changes, the provider should perform the changes in stop/start context. I'm willing to implement the fix, but please advise on proper behaviour here.

Relevant Error/Panic Output Snippet

Error: updating EC2 Instance (i-0db1177c4c05dc826) type: starting EC2 Instance (i-0db1177c4c05dc826): ReservationCapacityExceeded: The requested reservation does not have sufficient compatible and available capacity for this request.
status code: 400, request id: 21debb5c-604d-4c37-85d5-9cc4ff1cfd30

Terraform Configuration Files

provider "aws" {
  region = "eu-central-1"
}

variable "type" {
  default = "t3.micro"
}

resource "aws_ec2_capacity_reservation" "this" {
  availability_zone       = "eu-central-1c"
  instance_count          = 1
  instance_platform       = "Linux/UNIX"
  instance_type           = var.type
  instance_match_criteria = "targeted"
  end_date_type           = "unlimited"
  lifecycle {
    create_before_destroy = true
  }
}

resource "aws_instance" "this" {
  subnet_id     = "subnet-097a46cecc9ab465b"
  ami           = "ami-02957594f30581e82"
  instance_type = var.type
  capacity_reservation_specification {
    capacity_reservation_target {
      capacity_reservation_id = aws_ec2_capacity_reservation.this.id
    }
  }
}

Steps to Reproduce

• terraform apply (success)
• terraform apply -var type=t3.small (error)

Debug Output

No response

Panic Output

No response

Important Factoids

No response

References

No response

Would you like to implement a fix?

Yes

[github-actions]

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[github-actions]

This functionality has been released in v5.37.0 of the Terraform AWS Provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

For further feature requests or bug reports with this functionality, please create a new GitHub issue following the template. Thank you!

[github-actions]

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