How to fix Error: null_resource.provisioner not supported in Terraform

First, verify which version of Terraform you're running:

terraform version

If you're on Terraform 1.4 or later, null_resource is deprecated in favor of terraform_data. Ensure your version is fully up to date.

Convert your null_resource blocks to terraform_data. The syntax is nearly identical, with two key changes:
- Change resource "null_resource" to resource "terraform_data"
- Change the trigger argument from triggers to triggers_replace

Before (deprecated):

resource "null_resource" "example" {
  triggers = {
    instance_id = aws_instance.web.id
  }

  provisioner "local-exec" {
    command = "echo 'Instance created'"
  }
}

After (current best practice):

resource "terraform_data" "example" {
  triggers_replace = aws_instance.web.id

  provisioner "local-exec" {
    command = "echo 'Instance created'"
  }
}

Since terraform_data is built into Terraform, you no longer need to require the null provider. Remove or update your required_providers block:

Remove this:

terraform {
  required_providers {
    null = {
      source  = "hashicorp/null"
      version = "~> 3.0"
    }
  }
}

The terraform_data resource uses the built-in terraform provider, which is always available.

After updating your configuration, reinitialize to apply the changes:

terraform init

This will remove the null provider from your lock file and state if it's no longer referenced.

Verify that your updated configuration is valid and plan your changes:

terraform validate
terraform plan

Review the plan to ensure Terraform recognizes your terraform_data resources correctly and doesn't attempt to destroy and recreate your infrastructure.

Before applying, consider whether provisioners are necessary. HashiCorp recommends exhausting alternatives first:

- AWS: Use user_data scripts, Systems Manager Run Command, or CloudFormation templates
- Azure: Use Custom Script Extension or Azure Automation
- GCP: Use startup scripts or Cloud Build
- General: Use cloud-init, Ansible, Chef, or other configuration management tools

Provisioners are inherently less reliable than native cloud features and should be a last resort.