code: def get_docker_image(docker_override):
      """
      Get the docker image to use for the head node and worker nodes.
  
      Args:
          docker_override: The value of the --docker-override flag.
  
      Returns:
          The docker image to use for the head node and worker nodes, or None if not
          applicable.
      """
      if docker_override == "latest":
          return "rayproject/ray:latest-py38"
      elif docker_override == "nightly":
          return "rayproject/ray:nightly-py38"
      elif docker_override == "commit":
          if re.match("^[0-9]+.[0-9]+.[0-9]+$", ray.__version__):
              return f"rayproject/ray:{ray.__version__}.{ray.__commit__[:6]}-py38"
          else:
              print(
                  "Error: docker image is only available for "
                  f"release version, but we get: {ray.__version__}"
              )
              sys.exit(1)
      return None
  
imports: import argparse
  import os
  import re
  import subprocess
  import sys
  import tempfile
  import time
  import traceback
  from pathlib import Path
  import boto3
  import yaml
  from google.cloud import storage
  import ray
label_desc: Use image node_id 2 for calling a global function with example usage: get_docker_image(docker_override) and returns: None, str, str, str, ray, str, ray, str