Source code for airflow.executors.celery_executor

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.. seealso::
    For more information on how the CeleryExecutor works, take a look at the guide:
import logging
import math
import os
import subprocess
import time
import traceback
from multiprocessing import Pool, cpu_count

from celery import Celery
from celery import states as celery_states

from airflow.configuration import conf
from airflow.config_templates.default_celery import DEFAULT_CELERY_CONFIG
from airflow.exceptions import AirflowException
from airflow.executors.base_executor import BaseExecutor
from airflow.utils.module_loading import import_string
from airflow.utils.timeout import timeout

[docs]log = logging.getLogger(__name__)
# Make it constant for unit test.
[docs]CELERY_FETCH_ERR_MSG_HEADER = 'Error fetching Celery task state'
[docs]CELERY_SEND_ERR_MSG_HEADER = 'Error sending Celery task'
[docs]OPERATION_TIMEOUT = conf.getint('celery', 'operation_timeout', fallback=2)
''' To start the celery worker, run the command: airflow worker ''' if conf.has_option('celery', 'celery_config_options'):
[docs] celery_configuration = import_string( conf.get('celery', 'celery_config_options')
) else: celery_configuration = DEFAULT_CELERY_CONFIG
[docs]app = Celery( conf.get('celery', 'CELERY_APP_NAME'), config_source=celery_configuration)
[docs]def execute_command(command_to_exec): """Executes command.""" if command_to_exec[0:2] != ["airflow", "run"]: raise ValueError('The command must start with ["airflow", "run"].')"Executing command in Celery: %s", command_to_exec) env = os.environ.copy() try: subprocess.check_call(command_to_exec, stderr=subprocess.STDOUT, close_fds=True, env=env) except subprocess.CalledProcessError as e: log.exception('execute_command encountered a CalledProcessError') log.error(e.output) raise AirflowException('Celery command failed')
[docs]class ExceptionWithTraceback(object): """ Wrapper class used to propagate exceptions to parent processes from subprocesses. :param exception: The exception to wrap :type exception: Exception :param exception_traceback: The stacktrace to wrap :type exception_traceback: str """ def __init__(self, exception, exception_traceback): self.exception = exception self.traceback = exception_traceback
[docs]def fetch_celery_task_state(celery_task): """ Fetch and return the state of the given celery task. The scope of this function is global so that it can be called by subprocesses in the pool. :param celery_task: a tuple of the Celery task key and the async Celery object used to fetch the task's state :type celery_task: tuple(str, celery.result.AsyncResult) :return: a tuple of the Celery task key and the Celery state of the task :rtype: tuple[str, str] """ try: with timeout(seconds=OPERATION_TIMEOUT): # Accessing state property of celery task will make actual network request # to get the current state of the task. res = (celery_task[0], celery_task[1].state) except Exception as e: exception_traceback = "Celery Task ID: {}\n{}".format(celery_task[0], traceback.format_exc()) res = ExceptionWithTraceback(e, exception_traceback) return res
[docs]def send_task_to_executor(task_tuple): key, simple_ti, command, queue, task = task_tuple try: with timeout(seconds=OPERATION_TIMEOUT): result = task.apply_async(args=[command], queue=queue) except Exception as e: exception_traceback = "Celery Task ID: {}\n{}".format(key, traceback.format_exc()) result = ExceptionWithTraceback(e, exception_traceback) return key, command, result
[docs]class CeleryExecutor(BaseExecutor): """ CeleryExecutor is recommended for production use of Airflow. It allows distributing the execution of task instances to multiple worker nodes. Celery is a simple, flexible and reliable distributed system to process vast amounts of messages, while providing operations with the tools required to maintain such a system. """ def __init__(self): super(CeleryExecutor, self).__init__() # Celery doesn't support querying the state of multiple tasks in parallel # (which can become a bottleneck on bigger clusters) so we use # a multiprocessing pool to speed this up. # How many worker processes are created for checking celery task state. self._sync_parallelism = conf.getint('celery', 'SYNC_PARALLELISM') if self._sync_parallelism == 0: self._sync_parallelism = max(1, cpu_count() - 1) self._sync_pool = None self.tasks = {} self.last_state = {}
[docs] def start(self): self.log.debug( 'Starting Celery Executor using %s processes for syncing', self._sync_parallelism
[docs] def _num_tasks_per_send_process(self, to_send_count): """ How many Celery tasks should each worker process send. :return: Number of tasks that should be sent per process :rtype: int """ return max(1, int(math.ceil(1.0 * to_send_count / self._sync_parallelism)))
[docs] def _num_tasks_per_fetch_process(self): """ How many Celery tasks should be sent to each worker process. :return: Number of tasks that should be used per process :rtype: int """ return max(1, int(math.ceil(1.0 * len(self.tasks) / self._sync_parallelism)))
[docs] def trigger_tasks(self, open_slots): """ Overwrite trigger_tasks function from BaseExecutor :param open_slots: Number of open slots :return: """ sorted_queue = sorted( [(k, v) for k, v in self.queued_tasks.items()], key=lambda x: x[1][1], reverse=True) task_tuples_to_send = [] for i in range(min((open_slots, len(self.queued_tasks)))): key, (command, _, queue, simple_ti) = sorted_queue.pop(0) task_tuples_to_send.append((key, simple_ti, command, queue, execute_command)) cached_celery_backend = None if task_tuples_to_send: tasks = [t[4] for t in task_tuples_to_send] # Celery state queries will stuck if we do not use one same backend # for all tasks. cached_celery_backend = tasks[0].backend if task_tuples_to_send: # Use chunking instead of a work queue to reduce context switching # since tasks are roughly uniform in size chunksize = self._num_tasks_per_send_process(len(task_tuples_to_send)) num_processes = min(len(task_tuples_to_send), self._sync_parallelism) send_pool = Pool(processes=num_processes) key_and_async_results = send_task_to_executor, task_tuples_to_send, chunksize=chunksize) send_pool.close() send_pool.join() self.log.debug('Sent all tasks.') for key, command, result in key_and_async_results: if isinstance(result, ExceptionWithTraceback): self.log.error( # pylint: disable=logging-not-lazy CELERY_SEND_ERR_MSG_HEADER + ":%s\n%s\n", result.exception, result.traceback ) elif result is not None: # Only pops when enqueued successfully, otherwise keep it # and expect scheduler loop to deal with it. self.queued_tasks.pop(key) result.backend = cached_celery_backend self.running[key] = command self.tasks[key] = result self.last_state[key] = celery_states.PENDING
[docs] def sync(self): num_processes = min(len(self.tasks), self._sync_parallelism) if num_processes == 0: self.log.debug("No task to query celery, skipping sync") return self.log.debug("Inquiring about %s celery task(s) using %s processes", len(self.tasks), num_processes) # Recreate the process pool each sync in case processes in the pool die self._sync_pool = Pool(processes=num_processes) # Use chunking instead of a work queue to reduce context switching since tasks are # roughly uniform in size chunksize = self._num_tasks_per_fetch_process() self.log.debug("Waiting for inquiries to complete...") task_keys_to_states = fetch_celery_task_state, self.tasks.items(), chunksize=chunksize) self._sync_pool.close() self._sync_pool.join() self.log.debug("Inquiries completed.") for key_and_state in task_keys_to_states: if isinstance(key_and_state, ExceptionWithTraceback): self.log.error( # pylint: disable=logging-not-lazy CELERY_FETCH_ERR_MSG_HEADER + ", ignoring it:%s\n%s\n", repr(key_and_state.exception), key_and_state.traceback ) continue key, state = key_and_state try: if self.last_state[key] != state: if state == celery_states.SUCCESS: self.success(key) del self.tasks[key] del self.last_state[key] elif state == celery_states.FAILURE: del self.tasks[key] del self.last_state[key] elif state == celery_states.REVOKED: del self.tasks[key] del self.last_state[key] else:"Unexpected state: %s", state) self.last_state[key] = state except Exception: self.log.exception("Error syncing the Celery executor, ignoring it.")
[docs] def end(self, synchronous=False): if synchronous: while any([ task.state not in celery_states.READY_STATES for task in self.tasks.values()]): time.sleep(5) self.sync()

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