code: def start_head_processes(self):
          
          logger.info(
              "Process STDOUT and STDERR is being redirected to {}.".format(
                  self._logs_dir))
          assert self._redis_address is None
          # If this is the head node, start the relevant head node processes.
          self.start_redis()
          self.start_monitor()
          self.start_raylet_monitor()
          # The dashboard is Python3.x only.
          if PY3 and self._ray_params.include_webui:
              self.start_dashboard()
docs: Start head processes on the node.