Migrating deprecated Terraform resources (part 2)

In my previous post, I showed how to migrate deprecated Terraform resources to a supported resource type. But I hinted that there are some gotchas to be aware of. Here are some issues that I have encountered and how to work around them.

Deploying to a new environment

The import statement will fail if you try to deploy to a brand new empty environment. It makes sense when you think about it - how can you import a resource that doesn’t exist yet? Unfortunately, there’s no way to make the import statement conditional.

An example of this would be if your application has been in development for a while, and to assist in testing you now want to create a new UAT environment. There are no resources in the UAT environment yet, so the import statement will fail.

Initializing plugins and modules...
data.azurerm_resource_group.group: Refreshing...
data.azurerm_client_config.client: Refreshing...
data.azurerm_client_config.client: Refresh complete after 0s [id=xxxxxxxxxxxxx=]
data.azurerm_resource_group.group: Refresh complete after 0s [id=/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/rg-tfupgrade-australiasoutheast]
azurerm_service_plan.plan: Refreshing state... [id=/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/rg-tfupgrade-australiasoutheast/providers/Microsoft.Web/serverfarms/plan-tfupgrade-australiasoutheast]
╷
│ Error: Cannot import non-existent remote object
│
│ While attempting to import an existing object to
│ "azurerm_service_plan.plan", the provider detected that no object exists
│ with the given id. Only pre-existing objects can be imported; check that
│ the id is correct and that it is associated with the provider's configured
│ region or endpoint, or use "terraform apply" to create a new remote object
│ for this resource.
╵
Operation failed: failed running terraform plan (exit 1)

Deploying to an environment where resources may have been deleted.

This is similar to the previous scenario. It’s one I’ve encountered where we have non-production environments where you want to “mothball” when they’re not being actively used to save money. We selectively delete resources, and then when the environment is needed we re-provision them. Again, the import statement will fail if it is referencing a deleted resource.

A Solution

The workaround to support these scenarios is to not use the import statement in your HCL code, but instead use the terraform import command. Because we’re calling the command from the command line, we can make it conditional. e.g.

if az appservice plan show --name plan-tfupgrade-australiasoutheast --resource-group $ARM_RESOURCE_GROUP --query id --output tsv > /dev/null 2>&1; then
  terraform import azurerm_service_plan.plan /subscriptions/$ARM_SUBSCRIPTION_ID/resourceGroups/$ARM_RESOURCE_GROUP/providers/Microsoft.Web/serverfarms/plan-tfupgrade-australiasoutheast
else
  echo "Resource plan-tfupgrade-australiasoutheast does not exist in Azure"
fi

Repeat this pattern for all resources that need to be imported. Also, take care when referencing the Azure resource names. They need to be correct for the detection code to work as expected!

It’s not quite as elegant as using the import statement in your HCL code, but it does the job.

Example output

Here’s an example of the output from the terraform import command:

data.azurerm_resource_group.group: Reading...
data.azurerm_client_config.client: Reading...
data.azurerm_client_config.client: Read complete after 0s [id=xxxxxxxxxxxx=]
data.azurerm_resource_group.group: Read complete after 0s [id=/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/rg-tfupgrade-australiasoutheast]
azurerm_service_plan.plan: Importing from ID "/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/rg-tfupgrade-australiasoutheast/providers/Microsoft.Web/serverfarms/plan-tfupgrade-australiasoutheast"...
azurerm_service_plan.plan: Import prepared!
  Prepared azurerm_service_plan for import
azurerm_service_plan.plan: Refreshing state... [id=/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/rg-tfupgrade-australiasoutheast/providers/Microsoft.Web/serverfarms/plan-tfupgrade-australiasoutheast]

Import successful!

And the resultant plan shows no additional changes are necessary, which is just what we like to see!

data.azurerm_resource_group.group: Reading...
data.azurerm_client_config.client: Reading...
data.azurerm_client_config.client: Read complete after 0s [id=xxxxxxxxxxxxx=]
data.azurerm_resource_group.group: Read complete after 0s [id=/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/rg-tfupgrade-australiasoutheast]
azurerm_service_plan.plan: Refreshing state... [id=/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/rg-tfupgrade-australiasoutheast/providers/Microsoft.Web/serverfarms/plan-tfupgrade-australiasoutheast]
azurerm_linux_web_app.appservice: Refreshing state... [id=/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/rg-tfupgrade-australiasoutheast/providers/Microsoft.Web/sites/appservice-tfupgrade-australiasoutheast]

No changes. Your infrastructure matches the configuration.

Terraform has compared your real infrastructure against your configuration
and found no differences, so no changes are needed.

And if we apply this to an empty environment, it also runs successfully!

azurerm_service_plan.plan: Creating...
azurerm_service_plan.plan: Still creating... [10s elapsed]
azurerm_service_plan.plan: Creation complete after 10s [id=/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/rg-tfupgrade-australiasoutheast/providers/Microsoft.Web/serverfarms/plan-tfupgrade-australiasoutheast]
azurerm_linux_web_app.appservice: Creating...
azurerm_linux_web_app.appservice: Still creating... [10s elapsed]
azurerm_linux_web_app.appservice: Still creating... [20s elapsed]
azurerm_linux_web_app.appservice: Still creating... [30s elapsed]
azurerm_linux_web_app.appservice: Still creating... [40s elapsed]
azurerm_linux_web_app.appservice: Still creating... [50s elapsed]
azurerm_linux_web_app.appservice: Creation complete after 56s [id=/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/rg-tfupgrade-australiasoutheast/providers/Microsoft.Web/sites/appservice-tfupgrade-australiasoutheast]

Apply complete! Resources: 2 added, 0 changed, 0 destroyed.

Post-migration clean up

Whether you use the import statement or the terraform import command, once you’ve migrated your Terraform resources in all existing environments, I recommend you remove the migration code from HCL and pipeline YAML files.

Remove the import statements as they have no further purpose, and you only risk encountering the issue mentioned above if you ever want to deploy to a new environment.

There’s less risk of leaving the conditional terraform import commands in the pipeline YAML files, but as long as they remain they are slowing the pipeline down. Remove them to keep your pipelines running as fast as possible and to keep your YAML files as simple as possible. If you ever need to do another migration in the future, you’ll have the commands in your source control history to refer to.

Migrating deprecated Terraform resources

One of the challenges with using Terraform for your infrastructure as code is that the providers (that interact with cloud providers like Azure) are updated very frequently, and especially with major version releases this includes deprecating specific resource types. For example, when the Azure provider (AzureRM) version 3.0 was released, it deprecated many resource types and data sources. Some of these still exist in version 3, but are deprecated, will not receive any updates, and will be removed in version 4. Others have already been removed entirely.

I’ve created an example repo that demonstrates the migration process outlined here. Find it at https://github.com/flcdrg/terraform-azure-upgrade-resources.

While this post uses Azure and Azure Pipelines, the same principles should apply for other cloud providers and CI/CD systems.

To set the scene, here’s some Terraform code that creates an Azure App Service Plan and an App Service (src). The resource types are from v2.x AzureRM provider. Bear in mind, the last release of v2 was v2.99.0 in March 2022.

# https://registry.terraform.io/providers/hashicorp/azurerm/2.99.0/docs/resources/app_service_plan
resource "azurerm_app_service_plan" "plan" {
  name                = "plan-tfupgrade-australiasoutheast"
  resource_group_name = data.azurerm_resource_group.group.name
  location            = data.azurerm_resource_group.group.location
  kind                = "Linux"
  reserved            = true
  sku {
    tier = "Basic"
    size = "B1"
  }
}

# https://registry.terraform.io/providers/hashicorp/azurerm/latest/docs/resources/app_service
resource "azurerm_app_service" "appservice" {
  app_service_plan_id = azurerm_app_service_plan.plan.id
  name                = "appservice-tfupgrade-australiasoutheast"
  location            = data.azurerm_resource_group.group.location
  resource_group_name = data.azurerm_resource_group.group.name
  https_only          = true

  app_settings = {
    "TEST" = "TEST"
  }

  site_config {
    always_on                 = true
    ftps_state                = "Disabled"
    http2_enabled             = true
    linux_fx_version          = "DOTNETCORE|6.0"
    min_tls_version           = "1.2"
    use_32_bit_worker_process = false
  }
  identity {
    type = "SystemAssigned"
  }
}

The documentation for AzureRM v3.x shows that these resource types are deprecated and will be completely removed in v4.x. In addition, as these resource types are not being updated, they don’t support the latest features of Azure App Services, such as the new .NET 8 runtime.

So how can we switch to the azurerm_service_plan and azurerm_linux_web_app resource types?

You might think it’s just a matter of just changing the resource types and updating a few properties. But if you tried that you’ll discover that Terraform will try to delete the existing resources and create new ones. This is because the resource types are different, and Terraform doesn’t know that they are actually the same thing because the state representation of those resources is different.

Instead, we need to let Terraform know that the Azure resources that have already been created map to the new Terraform resource types we’ve defined in our configuration. In addition, we want to do this in a testable way using a pull request to verify that our changes look correct before we merge them into the main branch.

The approach we’ll take is to make use of the relatively new import block language feature. (In a future blog post I’ll cover when you might consider using the terraform import CLI command instead).

By using the import block, we can tell Terraform that the existing resources in Azure should be mapped to the new resource types we’ve defined in Terraform configuration. This means that Terraform will not try to delete the existing resources and create new ones. Instead, it will update the existing resources to match the Terraform configuration.

In the following example, we’re indicating that the Azure resource with the resource ID /subscriptions/.../resourceGroups/rg-tfupgrade-australiasoutheast/providers/Microsoft.Web/serverfarms/plan-tfupgrade-australiasoutheast should be mapped to the azurerm_service_plan resource type. Note the use of the data block reference to insert the subscription ID, rather than hard-coding it.

import {
  id = "/subscriptions/${data.azurerm_client_config.client.subscription_id}/resourceGroups/rg-tfupgrade-australiasoutheast/providers/Microsoft.Web/serverfarms/plan-tfupgrade-australiasoutheast"
  to = azurerm_service_plan.plan
}

resource "azurerm_service_plan" "plan" {
  name                = "plan-tfupgrade-australiasoutheast"
  resource_group_name = data.azurerm_resource_group.group.name
  location            = data.azurerm_resource_group.group.location
  sku_name            = "B1"
  os_type             = "Linux"
}

Often when you’re adding the new resource, the property names and ‘shape’ will change. Sometimes it’s pretty easy to figure out the equivalent, but sometimes you might need some help. One option you can utilise is generating the configuration.

In this case, you add the import block, but don’t add the resource block. If you then run terraform plan -generate-config-out=generated_resources.tf. Terraform will create a new file generated_resources.tf which will contain generated resources. You can then copy/paste those over into your regular .tf files. You’ll almost certainly want to edit them to remove redundant settings and replace hard-coded values with variable references where applicable. If you’re doing this as part of a pipeline, publish the generated file as a build artifact, so you can download it and incorporate the changes. You could make this an optional part of the pipeline that is enabled by setting a pipeline parameter to true.

There’s still one problem to solve though. While we’ve mapped the new resource types to the existing resources, Terraform state still knows about the old resource types, and will try to delete them now that they are no longer defined in the Terraform configuration. To solve this, we can use the terraform state rm command to remove the old resources from state. If they’re not in state, then Terraform doesn’t know about them and won’t try to delete them.

The following script will remove the old resources from state if they exist. Note that the terraform state rm command will fail if the resource doesn’t exist in state, so we need to check for the existence of the resource first.

# Remove state of old resources from Terraform
mapfile -t RESOURCES < <( terraform state list )

if [[ " ${RESOURCES[@]} " =~ "azurerm_app_service_plan.plan" ]]; then
  terraform state rm azurerm_app_service_plan.plan
fi

if [[ " ${RESOURCES[@]} " =~ "azurerm_app_service.appservice" ]]; then
  terraform state rm azurerm_app_service.appservice
fi

You will need to add an entry in this script for each Terraform resource type that you are removing.

Testing

Ok, so we have a strategy for upgrading our Terraform resources. But how do we test it? We don’t want to just merge the changes into the main branch and hope for the best. We want to test it first, and do this in isolation from other changes that might be happening in the main branch (or other branches). To test our changes need to update the Terraform state. But if we update the state used by everyone else then we won’t be popular when their builds start failing because Terraform will be trying to recreate resources that we’ve just deleted from state. Except those resources still exist in Azure!

What we want is a local copy of the Terraform state that we can try out our changes in without affecting anyone else. One way to do this is to copy the remote state to a local file, then reinitialise Terraform to use the ‘local’ backend. Obviously we won’t do a real deployment using this, but it is perfect for running terraform plan against.

Here’s an example script that will copy the remote state to a local file, then reinitialise Terraform to use the local backend. It assumes that your backend configuration is defined separately in a backend.tf file. Normally this would be pointing to a remote backend (e.g. Terraform Cloud or an Azure Storage account), within the pipeline run we replace this file with configuration to use a local backend.

terraform state pull > $(Build.ArtifactStagingDirectory)/pull.tfstate

cat > backend.tf <<EOF
terraform {
  backend "local" {
    path = "$(Build.ArtifactStagingDirectory)/pull.tfstate"
  }
}
EOF

# Reset Terraform to use local backend
terraform init -reconfigure -no-color -input=false

We now should have all the pieces in place to test our changes on PR build, and then once we’re happy with the plan, merge the changes and run the migration for real. If you have multiple environments (dev/test/prod) then you can roll this out to each environment as part of the normal release process.

For Azure Pipelines, we make use of conditional expressions, so that on PR builds we test the migration using local state, but on the main branch we modify the remote state and actually apply the changes.

Here’s the Azure Pipeline in full (src):

trigger: none

pr:
  branches:
    include:
      - main

pool:
  vmImage: ubuntu-latest

variables:
  - group: Terraform-Token

jobs:
  - job: build
    displayName: "Test Terraform Upgrade"

    variables:
      TerraformSourceDirectory: $(System.DefaultWorkingDirectory)/v3

    steps:
      - script: echo "##vso[task.setvariable variable=TF_TOKEN_app_terraform_io]$(TF_TOKEN)"
        displayName: "Terraform Token"

      - task: TerraformInstaller@2
        displayName: "Terraform: Installer"
        inputs:
          terraformVersion: "latest"

      - task: TerraformCLI@2
        displayName: "Terraform: init"
        inputs:
          command: init
          workingDirectory: "$(TerraformSourceDirectory)"
          backendType: selfConfigured
          commandOptions: -no-color -input=false
          allowTelemetryCollection: false

      - ${{ if ne(variables['Build.SourceBranch'], 'refs/heads/main') }}:
          # Copy state from Terraform Cloud to local, so we can modify it without affecting the remote state
          - script: |
              terraform state pull > $(Build.ArtifactStagingDirectory)/pull.tfstate

              # Write multiple lines of text to local file using bash
              cat > backend.tf <<EOF
              terraform {
                backend "local" {
                  path = "$(Build.ArtifactStagingDirectory)/pull.tfstate"
                }
              }
              EOF

              # Reset Terraform to use local backend
              terraform init -reconfigure -no-color -input=false
            displayName: "Script: Use Terraform Local Backend"
            workingDirectory: $(TerraformSourceDirectory)

      - script: |
          # Remove state of old resources from Terraform
          mapfile -t RESOURCES < <( terraform state list )

          if [[ " ${RESOURCES[@]} " =~ "azurerm_app_service_plan.plan" ]]; then
            terraform state rm azurerm_app_service_plan.plan
          fi

          if [[ " ${RESOURCES[@]} " =~ "azurerm_app_service.appservice" ]]; then
            terraform state rm azurerm_app_service.appservice
          fi
        displayName: "Script: Remove old resources from Terraform State"
        workingDirectory: $(TerraformSourceDirectory)

      - task: TerraformCLI@2
        displayName: "Terraform: validate"
        inputs:
          command: validate
          workingDirectory: "$(TerraformSourceDirectory)"
          commandOptions: -no-color

      - ${{ if ne(variables['Build.SourceBranch'], 'refs/heads/main') }}:
          - task: TerraformCLI@2
            displayName: "Terraform: plan"
            inputs:
              command: plan
              workingDirectory: "$(TerraformSourceDirectory)"
              commandOptions: -no-color -input=false -detailed-exitcode
              environmentServiceName: Azure MSDN - rg-tfupgrade-australiasoutheast
              publishPlanResults: Plan
              allowTelemetryCollection: false

      - ${{ if eq(variables['Build.SourceBranch'], 'refs/heads/main') }}:
          - task: TerraformCLI@2
            displayName: "Terraform: apply"
            inputs:
              command: apply
              workingDirectory: "$(TerraformSourceDirectory)"
              commandOptions: -no-color -input=false -auto-approve
              allowTelemetryCollection: false

Using it in practise

Ideally when you migrate the resource types, there will be no changes to the properties (and Terraform will report that no changes need to be made). Often the new resource type provides additional properties that you can take advantage of. Whether you set this initially or in a subsequent PR is up to you.

Here’s an example output from terraform plan:

Terraform v1.6.4
on linux_amd64
Initializing plugins and modules...
data.azurerm_resource_group.group: Refreshing...
data.azurerm_client_config.client: Refreshing...
data.azurerm_client_config.client: Refresh complete after 0s [id=xxxxxxxxxxx=]
data.azurerm_resource_group.group: Refresh complete after 0s [id=/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/rg-tfupgrade-australiasoutheast]
azurerm_service_plan.plan: Refreshing state... [id=/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/rg-tfupgrade-australiasoutheast/providers/Microsoft.Web/serverfarms/plan-tfupgrade-australiasoutheast]
azurerm_linux_web_app.appservice: Refreshing state... [id=/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/rg-tfupgrade-australiasoutheast/providers/Microsoft.Web/sites/appservice-tfupgrade-australiasoutheast]

Terraform will perform the following actions:

  # azurerm_linux_web_app.appservice will be imported
    resource "azurerm_linux_web_app" "appservice" {
        app_settings                                   = {
            "TEST" = "TEST"
        }
        client_affinity_enabled                        = false
        client_certificate_enabled                     = false
        client_certificate_mode                        = "Required"
        custom_domain_verification_id                  = (sensitive value)
        default_hostname                               = "appservice-tfupgrade-australiasoutheast.azurewebsites.net"
        enabled                                        = true
        ftp_publish_basic_authentication_enabled       = true
        https_only                                     = true
        id                                             = "/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/rg-tfupgrade-australiasoutheast/providers/Microsoft.Web/sites/appservice-tfupgrade-australiasoutheast"
        key_vault_reference_identity_id                = "SystemAssigned"
        kind                                           = "app,linux"
        location                                       = "australiasoutheast"
        name                                           = "appservice-tfupgrade-australiasoutheast"
        outbound_ip_address_list                       = [
            "52.189.223.107",
            "13.77.42.25",
            "13.77.46.217",
            "52.189.221.141",
            "13.77.50.99",
        ]
        outbound_ip_addresses                          = "52.189.223.107,13.77.42.25,13.77.46.217,52.189.221.141,13.77.50.99"
        possible_outbound_ip_address_list              = [
            "52.189.223.107",
            "13.77.42.25",
            "13.77.46.217",
            "52.189.221.141",
            "52.243.85.201",
            "52.243.85.94",
            "52.189.234.152",
            "13.77.56.61",
            "52.189.214.112",
            "20.11.210.198",
            "20.211.233.197",
            "20.211.238.191",
            "20.11.210.187",
            "20.11.211.1",
            "20.11.211.80",
            "4.198.70.38",
            "20.92.41.250",
            "4.198.68.27",
            "4.198.68.42",
            "20.92.47.59",
            "20.92.42.78",
            "13.77.50.99",
        ]
        possible_outbound_ip_addresses                 = "52.189.223.107,13.77.42.25,13.77.46.217,52.189.221.141,52.243.85.201,52.243.85.94,52.189.234.152,13.77.56.61,52.189.214.112,20.11.210.198,20.211.233.197,20.211.238.191,20.11.210.187,20.11.211.1,20.11.211.80,4.198.70.38,20.92.41.250,4.198.68.27,4.198.68.42,20.92.47.59,20.92.42.78,13.77.50.99"
        public_network_access_enabled                  = true
        resource_group_name                            = "rg-tfupgrade-australiasoutheast"
        service_plan_id                                = "/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/rg-tfupgrade-australiasoutheast/providers/Microsoft.Web/serverfarms/plan-tfupgrade-australiasoutheast"
        site_credential                                = (sensitive value)
        tags                                           = {}
        webdeploy_publish_basic_authentication_enabled = true

        identity {
            identity_ids = []
            principal_id = "a71e1fd5-e61b-4591-a439-98bad90cc837"
            tenant_id    = "59b0934d-4f35-4bff-a2b7-a451fe5f8bd6"
            type         = "SystemAssigned"
        }

        site_config {
            always_on                               = true
            auto_heal_enabled                       = false
            container_registry_use_managed_identity = false
            default_documents                       = []
            detailed_error_logging_enabled          = false
            ftps_state                              = "Disabled"
            health_check_eviction_time_in_min       = 0
            http2_enabled                           = true
            linux_fx_version                        = "DOTNETCORE|6.0"
            load_balancing_mode                     = "LeastRequests"
            local_mysql_enabled                     = false
            managed_pipeline_mode                   = "Integrated"
            minimum_tls_version                     = "1.2"
            remote_debugging_enabled                = false
            remote_debugging_version                = "VS2019"
            scm_minimum_tls_version                 = "1.2"
            scm_type                                = "VSTSRM"
            scm_use_main_ip_restriction             = false
            use_32_bit_worker                       = false
            vnet_route_all_enabled                  = false
            websockets_enabled                      = false
            worker_count                            = 1

            application_stack {
                docker_registry_password = (sensitive value)
                dotnet_version           = "6.0"
            }
        }
    }

  # azurerm_service_plan.plan will be imported
    resource "azurerm_service_plan" "plan" {
        id                           = "/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/rg-tfupgrade-australiasoutheast/providers/Microsoft.Web/serverfarms/plan-tfupgrade-australiasoutheast"
        kind                         = "linux"
        location                     = "australiasoutheast"
        maximum_elastic_worker_count = 1
        name                         = "plan-tfupgrade-australiasoutheast"
        os_type                      = "Linux"
        per_site_scaling_enabled     = false
        reserved                     = true
        resource_group_name          = "rg-tfupgrade-australiasoutheast"
        sku_name                     = "B1"
        tags                         = {}
        worker_count                 = 1
        zone_balancing_enabled       = false
    }

Plan: 2 to import, 0 to add, 0 to change, 0 to destroy.

In the next post, I’ll cover a few things to watch out for, and some post-migration clean up steps.

Terraform command 'init' failed with exit code '1'

I’m setting up a new GitHub repo to demonstrate using Terraform with Azure Pipelines via the CLI and I hit a weird error right at the start. I was using Jason Johnson’s Azure Pipelines Terraform Tasks extension like this:

- task: TerraformCLI@2
  inputs:
    command: init
    workingDirectory: "$(System.DefaultWorkingDirectory)/v2"
    backendType: selfConfigured
    commandOptions: -no-color -input=false
    allowTelemetryCollection: false

and it kept failing with the error:

/opt/hostedtoolcache/terraform/1.6.4/x64/terraform version
Terraform v1.6.4
on linux_amd64
+ provider registry.terraform.io/hashicorp/azurerm v2.99.0
+ provider registry.terraform.io/hashicorp/random v3.5.1
/opt/hostedtoolcache/terraform/1.6.4/x64/terraform init --input=false --no-color
Usage: terraform [global options] init [options]
...
Terraform command 'init' failed with exit code '1'.

I tried all sorts of things. It looked identical to other pipelines I had working (and ones I’d seen online). Was there a weird invisible character being passed on the command line? Out of desperation I copied the commandOptions line from another pipeline (which looked identical except that the arguments were in a different order).

But when I looked at the diff, not only were the arguments different, I realised that the dashes were different too! Terraform CLI arguments use a single dash, not a double dash. So the correct line is

commandOptions: -no-color -input=false

In hindsight, I realised that this is the first pipeline I’ve written on GitHub using the Terraform CLI (e.g. not in a work context) and so I did it manually, rather than copy/pasting from an existing (working) pipeline. A pity Terraform doesn’t support double dashes, but there you go.