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.
Categories: Azure Pipelines, DevOps