How to fix cpu_options.0.core_count conflicts with cpu_core_count in Terraform

Open your Terraform configuration file (main.tf, variables.tf, etc.) and search for the aws_instance resource block. Look for lines containing either:

Old (deprecated) method:

cpu_core_count       = 4
cpu_threads_per_core = 2

New method:

cpu_options {
  core_count       = 4
  threads_per_core = 2
}

Note whether you have one, both, or neither of these.

Delete the deprecated top-level arguments from your aws_instance resource. For example, change this:

resource "aws_instance" "example" {
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = "m5.large"
  cpu_core_count       = 4
  cpu_threads_per_core = 2
}

To this:

resource "aws_instance" "example" {
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = "m5.large"
}

If you need to specify custom CPU options, use the newer cpu_options block instead:

resource "aws_instance" "example" {
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = "m5.large"

  cpu_options {
    core_count       = 4
    threads_per_core = 2
  }
}

The cpu_options block must include both core_count and threads_per_core if you use it. These values are set at instance launch time and cannot be changed afterward.

Check that your aws_instance resource no longer has any of these deprecated arguments:
- cpu_core_count
- cpu_threads_per_core

Run a syntax check:

terraform validate

If the validate command succeeds without errors, your syntax is correct.

Execute a plan to confirm the error is gone:

terraform plan

If the plan succeeds without the conflicting configuration error, the issue is resolved. Review the proposed changes to ensure they match your intentions before applying.

If you're managing existing AWS infrastructure:

1. For new instances: The cpu_options block will be applied at creation time.

2. For existing instances: Terraform will not attempt to modify cpu_options after the instance is created (AWS does not support this). If you change cpu_options in your configuration, Terraform will require the instance to be destroyed and recreated.

To see what changes Terraform plans:

terraform plan -out=tfplan
terraform show tfplan

Review carefully before applying if it shows a resource must be replaced.