code: def get_ssh_key():
      
      path = os.environ.get("TUNE_CLUSTER_SSH_KEY",
                            os.path.expanduser("~/ray_bootstrap_key.pem"))
      if os.path.exists(path):
          return path
      return None
docs: Returns ssh key to connecting to cluster workers.
  
      If the env var TUNE_CLUSTER_SSH_KEY is provided, then this key
      will be used for syncing across different nodes.