Disable project-wide SSH keys for all instances

Explanation

Use of project-wide SSH keys means that a compromise of any one of these key pairs can result in all instances being compromised. It is recommended to use instance-level keys.

Possible Impact

Compromise of a single key pair compromises all instances

Suggested Resolution

Disable project-wide SSH keys

Insecure Example

The following example will fail the google-compute-no-project-wide-ssh-keys 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 = {
    block-project-ssh-keys = 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"]
  }
}

Secure Example

The following example will pass the google-compute-no-project-wide-ssh-keys 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 = {
    block-project-ssh-keys = 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"]
  }
}

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