Move compute instance's capacity reservation id change to the same request as shape

[b-dean]

Fixes #2313

Problem

If I have a compute instance and I want to change both its shape and its capacity reservation (to a different capacity reservation that I know has the new shape available), I can do that in the OCI web UI with a single update to the instance.

However, because of how those attributes are split apart in the terraform provider, it ends up being two different update requests. The first update request to change the shape will fail, because the current capacity reservation does not have sufficient capacity for the new shape.

terraform-provider-oci/internal/service/core/core_instance_resource.go

Lines 1470 to 1471 in 97b6ff8

	// Update shape, shape config, platform config, source details, fault domain and launch options
	err := s.updateOptionsViaWorkRequest()

The update to the new capacity reservation id doesn't happen until a later update request.

terraform-provider-oci/internal/service/core/core_instance_resource.go

Lines 1504 to 1507 in 97b6ff8

	if capacityReservationId, ok := s.D.GetOkExists("capacity_reservation_id"); ok {
	tmp := capacityReservationId.(string)
	request.CapacityReservationId = &tmp
	}

I believe, that capacity reservation id belongs in the first update (which contains shape, shape config, platform config, source details, fault domain, and launch options), because reserving capacity is intrinsically tied to the shape and shape config of the instance. You are reserving a specific shape.

Example

I have a complete working example in https://gist.github.com/b-dean/0cccde387e8dcc57167b08e5e45ef80c, which I referenced from #2313

In this example there's a capacity reservation with E4 instances and one with E5, and the instance will switch between them. Real world examples would likely be more complex, but the principle is still the same: it should be possible to change both shape and capacity reservation at the same time.

variable "shape_index" {
  type    = number
  default = 0
}

variable "shapes" {
  type = list(string)

  default = [
    "VM.Standard.E4.Flex",
    "VM.Standard.E5.Flex",
  ]
}

resource "oci_core_compute_capacity_reservation" "example" {
  count = length(var.shapes)

  availability_domain = var.availability_domain
  compartment_id      = var.compartment_id
  display_name        = "example-${count.index}"

  instance_reservation_configs {
    instance_shape = var.shapes[count.index]
    reserved_count = 1
    fault_domain   = var.fault_domain

    instance_shape_config {
      memory_in_gbs = 4
      ocpus         = 1
    }
  }
}

resource "oci_core_instance" "example" {
  availability_domain = var.availability_domain
  compartment_id      = var.compartment_id
  fault_domain   = var.fault_domain
  capacity_reservation_id = oci_core_compute_capacity_reservation.example[var.shape_index].id
  display_name            = "example"
  shape                   = var.shapes[var.shape_index]

  shape_config {
    memory_in_gbs = 4
    ocpus         = 1
  }
}

The first terraform apply puts it in the E4 capacity reservation:

terraform apply -var shape_index=0

The second should change the shape and move it to the new capacity reservation:

terraform apply -var shape_index=1

but it fails:

│ Error: 400-InvalidParameter, Invalid Shape Config: No valid reservation configs in the reservation to move the resize to.
│ Suggestion: Please update the parameter(s) in the Terraform config as per error message Invalid Shape Config: No valid reservation configs in the reservation to move the resize to.
│ Documentation: https://registry.terraform.io/providers/oracle/oci/latest/docs/resources/core_instance
│ API Reference: https://docs.oracle.com/iaas/api/#/en/iaas/20160918/Instance/UpdateInstance
│ Request Target: PUT https://iaas.us-ashburn-1.oraclecloud.com/20160918/instances/ocid1.instance.oc1.iad.xxxxxxxxxxxxxxxx
│ Provider version: 6.28.0, released on 2025-03-02.
│ Service: Core Instance
│ Operation Name: UpdateInstance
│ OPC request ID: xxxxxxxxxxxxxxxx
│
│
│   with oci_core_instance.example,
│   on main.tf line 46, in resource "oci_core_instance" "example":
│   46: resource "oci_core_instance" "example" {
│

Because it's trying to change only the shape, and there aren't any of that shape in the old capacity reservation.

When I build a local copy of the provider from this PR it is able to update both shape and capacity reservation at the same time.

[tf-oci-pub]

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