This document is for Celery's development version, which can be significantly different from previous releases. Get old docs here: 3.0.

Task Messages

Message format

• task

  string:

  Name of the task. required

• id

  string:

  Unique id of the task (UUID). required

• args

  list:

  List of arguments. Will be an empty list if not provided.

• kwargs

  dictionary:

  Dictionary of keyword arguments. Will be an empty dictionary if not provided.

• retries

  int:

  Current number of times this task has been retried. Defaults to 0 if not specified.

• eta

  string (ISO 8601):  

  Estimated time of arrival. This is the date and time in ISO 8601 format. If not provided the message is not scheduled, but will be executed asap.

• expires

  string (ISO 8601):  

  New in version 2.0.2.

  Expiration date. This is the date and time in ISO 8601 format. If not provided the message will never expire. The message will be expired when the message is received and the expiration date has been exceeded.

Extensions

Extensions are additional keys in the message body that the worker may or may not support. If the worker finds an extension key it doesn’t support it should optimally reject the message so another worker gets a chance to process it.

• taskset

  string:

  The taskset this task is part of (if any).

• chord

  subtask:

  New in version 2.3.

  Signifies that this task is one of the header parts of a chord. The value of this key is the body of the cord that should be executed when all of the tasks in the header has returned.

• utc

  bool:

  New in version 2.5.

  If true time uses the UTC timezone, if not the current local timezone should be used.

• callbacks

  <list>subtask:

  New in version 3.0.

  A list of subtasks to apply if the task exited successfully.

• errbacks

  <list>subtask:

  New in version 3.0.

  A list of subtasks to apply if an error occurs while executing the task.

• timeouts

  tuple:

  New in version 3.1.

  Task execution timeouts. This is a tuple of hard and soft timeouts. Timeout values are int or float.

Example message

This is an example invocation of the celery.task.PingTask task in JSON format:

{"id": "4cc7438e-afd4-4f8f-a2f3-f46567e7ca77",
 "task": "celery.task.PingTask",
 "args": [],
 "kwargs": {},
 "retries": 0,
 "eta": "2009-11-17T12:30:56.527191"}

Serialization

Several types of serialization formats are supported using the content_type message header.

The MIME-types supported by default are shown in the following table.

Scheme	MIME Type
json	application/json
yaml	application/x-yaml
pickle	application/x-python-serialize
msgpack	application/x-msgpack