code: def test_redis_failureover(
      redis_replicas, ray_start_cluster_head_with_external_redis
  ):
      """This test is to cover ray cluster's behavior when Redis master failed.
      The management of the Redis cluster is not covered by Ray, but Ray should handle
      the failure correctly.
      For this test we ensure:
      - When Redis master failed, Ray should crash (TODO: make ray automatically switch to
        new master).
      - After Redis recovered, Ray should be able to use the new Master.
      - When the master becomes slaves, Ray should crash.
      """
      cluster = ray_start_cluster_head_with_external_redis
      import redis
  
      redis_addr = os.environ.get("RAY_REDIS_ADDRESS")
      ip, port = redis_addr.split(":")
      redis_cli = redis.Redis(ip, port)
  
      def get_connected_nodes():
          return [
              (k, v)
              for (k, v) in redis_cli.cluster("nodes").items()
              if v["connected"]
          ]
  
      wait_for_condition(
          lambda: len(get_connected_nodes())
          == int(os.environ.get("TEST_EXTERNAL_REDIS_REPLICAS"))
      )
      nodes = redis_cli.cluster("nodes")
      leader_cli = None
      follower_cli = []
      for addr in nodes:
          ip, port = addr.split(":")
          cli = redis.Redis(ip, port)
          meta = nodes[addr]
          flags = meta["flags"].split(",")
          if "master" in flags:
              leader_cli = cli
              print("LEADER", addr, redis_addr)
          else:
              follower_cli.append(cli)
  
      leader_pid = leader_cli.info()["process_id"]
  
      @ray.remote(max_restarts=-1)
      class Counter:
          def r(self, v):
              return v
  
          def pid(self):
              import os
  
              return os.getpid()
  
      c = Counter.options(
          name="c", namespace="test", lifetime="detached"
      ).remote()
      c_pid = ray.get(c.pid.remote())
      c_process = psutil.Process(pid=c_pid)
      r = ray.get(c.r.remote(10))
      assert r == 10
  
      head_node = cluster.head_node
      gcs_server_process = head_node.all_processes["gcs_server"][
          0
      ].process
      gcs_server_pid = gcs_server_process.pid
  
      # Wait until all data is updated in the replica
      leader_cli.set("_hole", "0")
      wait_for_condition(
          lambda: all([b"_hole" in f.keys("*") for f in follower_cli])
      )
  
      # Now kill pid
      leader_process = psutil.Process(pid=leader_pid)
      leader_process.kill()
  
      print(">>> Waiting gcs server to exit", gcs_server_pid)
      wait_for_pid_to_exit(gcs_server_pid, 1000)
      print("GCS killed")
  
      follower_cli[0].cluster("failover", "takeover")
      wait_for_condition(
          lambda: len(get_connected_nodes())
          == int(os.environ.get("TEST_EXTERNAL_REDIS_REPLICAS")) - 1
      )
  
      # Kill Counter actor. It should restart after GCS is back
      c_process.kill()
      # Cleanup the in memory data and then start gcs
      cluster.head_node.kill_gcs_server(False)
  
      print("Start gcs")
      sleep(2)
      cluster.head_node.start_gcs_server()
  
      assert len(ray.nodes()) == 1
      assert ray.nodes()[0]["alive"]
  
      driver_script = f"""
  import ray
  ray.init('{cluster.address}')
  @ray.remote
  def f():
      return 10
  assert ray.get(f.remote()) == 10
  
  c = ray.get_actor("c", namespace="test")
  v = ray.get(c.r.remote(10))
  assert v == 10
  print("DONE")
  """
  
      # Make sure the cluster is usable
      wait_for_condition(
          lambda: "DONE" in run_string_as_driver(driver_script)
      )
  
      # Now make follower_cli[0] become replica
      # and promote follower_cli[1] as leader
      follower_cli[1].cluster("failover", "takeover")
      head_node = cluster.head_node
      gcs_server_process = head_node.all_processes["gcs_server"][
          0
      ].process
      gcs_server_pid = gcs_server_process.pid
      # GCS should exit in this case
      print(">>> Waiting gcs server to exit", gcs_server_pid)
      wait_for_pid_to_exit(gcs_server_pid, 10000)
  
imports: import sys
  import os
  import threading
  from time import sleep
  import pytest
  import ray
  from ray._private.utils import get_or_create_event_loop
  from ray.util.scheduling_strategies import PlacementGroupSchedulingStrategy
  import ray._private.gcs_utils
  from ray._private import ray_constants
  from ray._private.test_utils import convert_actor_state, enable_external_redis, generate_system_config_map, wait_for_condition, wait_for_pid_to_exit, run_string_as_driver
  from ray.job_submission import JobSubmissionClient, JobStatus
  from ray._raylet import GcsClient
  import psutil
label_desc: Use image node_id 19 for calling a global function with example usage: test_redis_failureover(redis_replicas, ray_start_cluster_head_with_external_redis) and returns: unknown, v, os