Celery任务状态报错一例

Celery 中定义FAILURE状态时，报错：KeyError: 'exc_type'，完整内容大致如下：

>>> print(task.state)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python3.6/site-packages/celery/result.py", line 471, in state
    return self._get_task_meta()['status']
  File "/usr/local/lib/python3.6/site-packages/celery/result.py", line 410, in _get_task_meta
    return self._maybe_set_cache(self.backend.get_task_meta(self.id))
  File "/usr/local/lib/python3.6/site-packages/celery/backends/base.py", line 359, in get_task_meta
    meta = self._get_task_meta_for(task_id)
  File "/usr/local/lib/python3.6/site-packages/celery/backends/base.py", line 674, in _get_task_meta_for
    return self.decode_result(meta)
  File "/usr/local/lib/python3.6/site-packages/celery/backends/base.py", line 278, in decode_result
    return self.meta_from_decoded(self.decode(payload))
  File "/usr/local/lib/python3.6/site-packages/celery/backends/base.py", line 274, in meta_from_decoded
    meta['result'] = self.exception_to_python(meta['result'])
  File "/usr/local/lib/python3.6/site-packages/celery/backends/base.py", line 248, in exception_to_python
    from_utf8(exc['exc_type']), __name__)
KeyError: 'exc_type'

这个报错主要是meta字段中缺少exc_type和exc_message关键字导致的，在meta中添加这两个关键字即可消除报错：

@app.task(bind=True)
def task(self):
    try:
        raise ValueError('Some error')
    except Exception as ex:
        self.update_state(
            state=states.FAILURE,
            meta={
                'exc_type': type(ex).__name__,
                'exc_message': traceback.format_exc().split('\n')
                'custom': '...'
            })
        raise Ignore()

需要注意的是，在使用返回response时就不能再使用task.info来返回内容了，需要使用如下文件返回：

>>> import tasks
>>> task = tasks.task.s().delay()
>>> print(task.state)
'FAILURE'
>>> print(task.info)
ValueError('Traceback (most recent call last):', '  File "/app/tasks.py", line 16, in task', "    raise ValueError('some exception')", 'ValueError: some exception', '')
>>> print(task.backend.get(task.backend.get_key_for_task(task.id)))
b'{"status": "FAILURE", "result": {"exc_type": "ValueError", "exc_message": ["Traceback (most recent call last):", "  File \\"/app/tasks.py\\", line 16, in task", "    raise ValueError(\'some exception\')", "ValueError: some exception", ""], "custom": "..."}, "traceback": null, "children": [], "task_id": "d2f60111-aec6-4c58-83a7-24f0edb7ac5f"}'
Custom state