Disable serial port connectivity for all instances

Explanation

When serial port access is enabled, the access is not governed by network security rules meaning the port can be exposed publicly.

Possible Impact

Unrestricted network access to the serial console of the instance

Suggested Resolution

Disable serial port access

Insecure Example

The following example will fail the google-compute-no-serial-port check.

resource "google_service_account" "default" {
  account_id   = "service_account_id"
  display_name = "Service Account"
}

resource "google_compute_instance" "default" {
  name         = "test"
  machine_type = "e2-medium"
  zone         = "us-central1-a"

  tags = ["foo", "bar"]

  boot_disk {
    initialize_params {
      image = "debian-cloud/debian-9"
    }
  }

  // Local SSD disk
  scratch_disk {
    interface = "SCSI"
  }

  network_interface {
    network = "default"

    access_config {
      // Ephemeral IP
    }
  }

  metadata = {
    serial-port-enable = true
  }

  metadata_startup_script = "echo hi > /test.txt"

  service_account {
    # Google recommends custom service accounts that have cloud-platform scope and permissions granted via IAM Roles.
    email  = google_service_account.default.email
    scopes = ["cloud-platform"]
  }
}

Secure Example

The following example will pass the google-compute-no-serial-port check.

resource "google_service_account" "default" {
  account_id   = "service_account_id"
  display_name = "Service Account"
}

resource "google_compute_instance" "default" {
  name         = "test"
  machine_type = "e2-medium"
  zone         = "us-central1-a"

  tags = ["foo", "bar"]

  boot_disk {
    initialize_params {
      image = "debian-cloud/debian-9"
    }
  }

  // Local SSD disk
  scratch_disk {
    interface = "SCSI"
  }

  network_interface {
    network = "default"

    access_config {
      // Ephemeral IP
    }
  }

  metadata = {
    serial-port-enable = false
  }

  metadata_startup_script = "echo hi > /test.txt"

  service_account {
    # Google recommends custom service accounts that have cloud-platform scope and permissions granted via IAM Roles.
    email  = google_service_account.default.email
    scopes = ["cloud-platform"]
  }
}

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