src/main/resources/org/apache/aurora/scheduler/tiers.json

{
  "tiers":
  {
    "preferred":
    {
      "preemptible": false,
      "revocable": false
    },
    "preemptible":
    {
      "preemptible": true,
      "revocable": false
    },
    "revocable":
    {
      "preemptible": true,
      "revocable": true
    }
  }
}