fix: Instance image diff during Instance import

[ezilber-akamai]

📝 Description

Fixed an import/migration diff where linode_instance_disk.image was missing from state, causing unnecessary updates.

✔️ How to Test

The following test steps assume you have pulled down this PR locally.

Integration Testing:

make test-int TEST_SUITE="instancedisk"

Manual Testing:

1. In a sandbox environment (i.e. dx-devenv), run make init followed by make apply for the following TF Configuration:

provider "linode" {}

resource "linode_instance" "test" {
  label  = "tf-disk-migration-test"
  region = "us-east"
  type   = "g6-standard-1"

  image = "linode/ubuntu22.04"
}

2. Ensure the instance is created successfully.
3. Run the following CLI commands and note the Disk and Config IDs:
   • linode-cli linodes disks-list <LINODE_ID>
   • linode-cli linodes configs-list <LINODE_ID>
4. Update the TF Configuration to the following:

provider "linode" {}

resource "linode_instance" "test" {
  label  = "tf-disk-migration-test"
  region = "us-east"
  type   = "g6-standard-1"

  image = "linode/ubuntu22.04"
}

resource "linode_instance_disk" "boot" {
  linode_id = linode_instance.test.id

  label = "linode-root"
  size  = 5120

  image = linode_instance.test.image
}

resource "linode_instance_config" "cfg" {
  linode_id = linode_instance.test.id
  label     = "My Ubuntu 22.04 LTS Disk Profile"

  device {
    device_name = "sda"
    disk_id     = linode_instance_disk.boot.id
  }
}

5. Run the following commands and ensure they run successfully:
   • terraform import linode_instance_disk.boot <LINODE_ID>,<DISK_ID>
   • terraform import linode_instance_config.cfg <LINODE_ID>,<CONFIG_ID>
6. Run make plan and ensure that no image diff is detected.
7. Clean up all dangling resources created for this test.

[Copilot]

Pull request overview

This PR fixes a state management issue where the image attribute was missing from the Terraform state during instance disk imports, causing unnecessary diffs and potential resource replacements.

Changes:

• Added UseStateForUnknown() plan modifier to preserve the image attribute in state
• Implemented logic to populate image from the parent instance during Read operations when the state value is null

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
linode/instancedisk/framework_resource_schema.go	Added plan modifier to preserve image state value
linode/instancedisk/framework_resource.go	Added logic to backfill image from parent instance during import

---

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[zliang-akamai]

This may introduce another issue when you are importing the disk without specifying image in the TF config:

provider "linode" {}

resource "linode_instance" "test" {
  label  = "tf-disk-migration-test"
  region = "us-east"
  type   = "g6-standard-1"

  image = "linode/ubuntu22.04"
}

resource "linode_instance_disk" "boot" {
  linode_id = linode_instance.test.id

  label = "Ubuntu 22.04 LTS Disk"
  size  = 50688
  // image removed here
}

resource "linode_instance_config" "cfg" {
  linode_id = linode_instance.test.id
  label     = "My Ubuntu 22.04 LTS Disk Profile"

  device {
    device_name = "sda"
    disk_id     = linode_instance_disk.boot.id
  }
}

OpenTofu used the selected providers to generate the following execution plan. Resource
actions are indicated with the following symbols:
  ~ update in-place (current -> planned)
-/+ destroy and then create replacement

OpenTofu will perform the following actions:

  # linode_instance_config.cfg will be updated in-place
  ~ resource "linode_instance_config" "cfg" {
        id           = "94245142"
      ~ kernel       = "linode/grub2" -> "linode/latest-64bit"
        # (7 unchanged attributes hidden)

      - device {
          - device_name = "sda" -> null
          - disk_id     = 172334734 -> null
          - volume_id   = 0 -> null
        }
      - device {
          - device_name = "sdb" -> null
          - disk_id     = 172334736 -> null
          - volume_id   = 0 -> null
        }
      + device {
          + device_name = "sda"
          + disk_id     = (known after apply)
        }

        # (2 unchanged blocks hidden)
    }

  # linode_instance_disk.boot must be replaced
-/+ resource "linode_instance_disk" "boot" {
      ~ created         = "2026-01-28T21:55:11Z" -> (known after apply)
      ~ disk_encryption = "enabled" -> (known after apply)
      ~ filesystem      = "ext4" -> (known after apply)
      ~ id              = "172334734" -> (known after apply)
      - image           = "linode/ubuntu22.04" -> null # forces replacement
      ~ status          = "ready" -> (known after apply)
      ~ updated         = "2026-01-28T21:56:19Z" -> (known after apply)
        # (3 unchanged attributes hidden)
    }

Plan: 1 to add, 1 to change, 1 to destroy.

──────────────────────────────────────────────────────────────────────────────────────────────

Note: You didn't use the -out option to save this plan, so OpenTofu can't guarantee to take
exactly these actions if you run "tofu apply" now.

[zliang-akamai]

LGTM!