add rolling restart

[knoguchi]

The Druid roles must be rolling restarted at the configuration change or Druid upgrade.

• Research what changes requires restart and which role, and the restart order
• Create restart graph?
• Execute the restart graph?

Example:

• realtime indexing node with 2 replicas (total 2), the two must not be restarted at the same time

[knoguchi]

• make sure replicas of the realtime indexing servers should not be restarted at the same time.
  • tasks are created for Kafka topic x partitions x replications
• Running tasks GET http://overlord:18081/druid/indexer/v1/runningTasks

  {
    "id": "index_realtime_DATASOURCE_2017-04-22T05:00:00.000Z_1_0",
    "createdTime": "2017-04-22T04:59:59.959Z",
    "queueInsertionTime": "2017-04-22T04:59:59.960Z",
    "location": {
      "host": "worker123",
      "port": 8101
    }
  },

• Pending tasks /druid/indexer/v1/pendingTasks
• Waiting tasks /druid/indexer/v1/waitingTasks
• workers /druid/indexer/v1/workers

  {
  "worker": {
    "host": "worker013:18091",
    "ip": "hworker013",
    "capacity": 2,
    "version": "0"
  },
  "currCapacityUsed": 2,
  "availabilityGroups": [
    "DATASOURCE-2017-04-22T04:00:00.000Z-0000",
    "DATASOURCE-2017-04-22T05:00:00.000Z-0000"
  ],
  "runningTasks": [
    "index_realtime_DATASOURCE_2017-04-22T04:00:00.000Z_0_0",
    "index_realtime_DATASOURCE_2017-04-22T05:00:00.000Z_0_0"
  ],
  "lastCompletedTaskTime": "2017-04-22T04:16:07.920Z"
  },