从任务中恢复失败超过 max_retries

Question

我正在尝试异步使用 Web 服务，因为它最多需要 45 秒才能返回。不幸的是，此 Web 服务也有些不可靠，并且可能会引发错误。我已经设置了django-celery 并执行了我的任务，它工作正常，直到任务失败超出max_retries。

这是我目前所拥有的：

@task(default_retry_delay=5, max_retries=10)
def request(xml):
    try:
        server = Client('https://www.whatever.net/RealTimeService.asmx?wsdl')
        xml = server.service.RunRealTimeXML(
            username=settings.WS_USERNAME,
            password=settings.WS_PASSWORD,
            xml=xml
        )
    except Exception, e:
        result = Result(celery_id=request.request.id, details=e.reason, status="i")
        result.save()
        try:
            return request.retry(exc=e)
        except MaxRetriesExceededError, e:
            result = Result(celery_id=request.request.id, details="Max Retries Exceeded", status="f")
            result.save()
            raise
    result = Result(celery_id=request.request.id, details=xml, status="s")
    result.save()
    return result

不幸的是，MaxRetriesExceededError 没有被retry() 抛出，所以我不确定如何处理此任务的失败。 Django 已经将 HTML 返回给客户端，我正在通过 AJAX 检查Result 的内容，这永远不会完全失败f 状态。

所以问题是：当 Celery 任务超过 max_retries 时，如何更新我的数据库？

Answer 1

你可以重写celery任务类的after_return方法，这个方法在任务执行后无论ret状态是什么(SUCCESS,FAILED,RETRY)都会被调用

class MyTask(celery.task.Task)

    def run(self, xml, **kwargs)
        #Your stuffs here

    def after_return(self, status, retval, task_id, args, kwargs, einfo=None):
        if self.max_retries == int(kwargs['task_retries']):
            #If max retries are equals to task retries do something
        if status == "FAILURE":
            #You can do also something if the tasks fail instead of check the retries

http://readthedocs.org/docs/celery/en/latest/reference/celery.task.base.html#celery.task.base.BaseTask.after_return

http://celery.readthedocs.org/en/latest/reference/celery.app.task.html?highlight=after_return#celery.app.task.Task.after_return

Answer 2

对于 Celery 2.3.2 版，这种方法对我来说效果很好：

class MyTask(celery.task.Task):
    abstract = True

    def after_return(self, status, retval, task_id, args, kwargs, einfo):
        if self.max_retries == self.request.retries:
            #If max retries is equal to task retries do something

@task(base=MyTask, default_retry_delay=5, max_retries=10)
def request(xml):
    #Your stuff here

Answer 3

我现在只是这样做，省去了子类化 Task 的工作，并且很容易理解。

# auto-retry with delay as defined below. After that, hook is disabled.
@celery.shared_task(bind=True, max_retries=5, default_retry_delay=300)
def post_data(self, hook_object_id, url, event, payload):
    headers = {'Content-type': 'application/json'}
    try:
        r = requests.post(url, data=payload, headers=headers)
        r.raise_for_status()
    except requests.exceptions.RequestException as e:
        if self.request.retries >= self.max_retries:
            log.warning("Auto-deactivating webhook %s for event %s", hook_object_id, event)
            Webhook.objects.filter(object_id=hook_object_id).update(active=False)
            return False
        raise self.retry(exc=e)
    return True

Answer 4

问题是 celery 在达到重试限制时试图重新引发您传入的异常。重新加注的代码在这里：https://github.com/celery/celery/blob/v3.1.20/celery/app/task.py#L673-L681

解决这个问题的最简单方法是根本不让 celery 管理您的异常：

@task(max_retries=10)
def mytask():
    try:
        do_the_thing()
    except Exception as e:
        try:
            mytask.retry()
        except MaxRetriesExceededError:
            do_something_to_handle_the_error()
            logger.exception(e)