This document describes the current stable version of Celery (5.2). For development docs, go here.
What’s new in Celery 5.1 (Sun Harmonics)¶
Josue Balandrano Coronel (
jbc at rmcomplexity.com)
Celery is a simple, flexible, and reliable distributed programming framework to process vast amounts of messages, while providing operations with the tools required to maintain a distributed system with python.
It’s a task queue with focus on real-time processing, while also supporting task scheduling.
To read more about Celery you should go read the introduction.
While this version is mostly backward compatible with previous versions it’s important that you read the following section as this release is a new major version.
This version is officially supported on CPython 3.6, 3.7 & 3.8 & 3.9 and is also supported on PyPy3.
Table of Contents
Make sure you read the important notes before upgrading to this version.
The 5.1.0 release is a new minor release for Celery.
Starting from now users should expect more frequent releases of major versions as we move fast and break things to bring you even better experience.
From now on we only support Python 3.6 and above. We will maintain compatibility with Python 3.6 until it’s EOL in December, 2021.
— Omer Katz
As we’d like to provide some time for you to transition, we’re designating Celery 4.x an LTS release. Celery 4.x will be supported until the 1st of August, 2021.
We will accept and apply patches for bug fixes and security issues. However, no new features will be merged for that version.
Celery 5.x is not an LTS release. We will support it until the release of Celery 6.x.
We’re in the process of defining our Long Term Support policy. Watch the next “What’s New” document for updates.
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Celery 5.0 introduces a new CLI implementation which isn’t completely backwards compatible.
The global options can no longer be positioned after the sub-command. Instead, they must be positioned as an option for the celery command like so:
celery --app path.to.app worker
If you were using our Daemonization guide to deploy Celery in production, you should revisit it for updates.
If you haven’t already updated your configuration when you migrated to Celery 4.0, please do so now.
We elected to extend the deprecation period until 6.0 since we did not loudly warn about using these deprecated settings.
Please refer to the migration guide for instructions.
Make sure you are not affected by any of the important upgrade notes mentioned in the following section.
You should verify that none of the breaking changes in the CLI do not affect you. Please refer to New Command Line Interface for details.
Celery 5.x only supports Python 3. Therefore, you must ensure your code is compatible with Python 3.
If you haven’t ported your code to Python 3, you must do so before upgrading.
After the migration is done, run your test suite with Celery 4 to ensure nothing has been broken.
The supported Python Versions are:
PyPy3.6 7.2 (
Starting from v5.1, the minimum required version is Kombu 5.1.0.
Starting from v5.1, the minimum required version is Billiard 3.6.4.
Dropped support for Python 2.7 & 3.5¶
Celery now requires Python 3.6 and above.
Python 2.7 has reached EOL in January 2020. In order to focus our efforts we have dropped support for Python 2.7 in this version.
In addition, Python 3.5 has reached EOL in September 2020. Therefore, we are also dropping support for Python 3.5.
If you still require to run Celery using Python 2.7 or Python 3.5 you can still use Celery 4.x. However we encourage you to upgrade to a supported Python version since no further security patches will be applied for Python 2.7 or Python 3.5.
Eventlet Workers Pool¶
Due to eventlet/eventlet#526 the minimum required version is eventlet 0.26.1.
Gevent Workers Pool¶
Starting from v5.0, the minimum required version is gevent 1.0.0.
Couchbase Result Backend¶
The Couchbase result backend now uses the V3 Couchbase SDK.
As a result, we no longer support Couchbase Server 5.x.
Also, starting from v5.0, the minimum required version for the database client is couchbase 3.0.0.
To verify that your Couchbase Server is compatible with the V3 SDK, please refer to their documentation.
Riak Result Backend¶
The Riak result backend has been removed as the database is no longer maintained.
The Python client only supports Python 3.6 and below which prevents us from supporting it and it is also unmaintained.
If you are still using Riak, refrain from upgrading to Celery 5.0 while you migrate your application to a different database.
We apologize for the lack of notice in advance but we feel that the chance you’ll be affected by this breaking change is minimal which is why we did it.
AMQP Result Backend¶
The AMQP result backend has been removed as it was deprecated in version 4.0.
Removed Deprecated Modules¶
The celery.utils.encoding and the celery.task modules has been deprecated in version 4.0 and therefore are removed in 5.0.
If you were using the celery.utils.encoding module before, you should import kombu.utils.encoding instead.
If you were using the celery.task module before, you should import directly from the celery module instead.
With Kombu v5.1.0 we now support Azure Services Bus.
Azure have completely changed the Azure ServiceBus SDK between 0.50.0 and 7.0.0. azure-servicebus >= 7.0.0 is now required for Kombu 5.1.0
Following the changes in SQLAlchemy 1.4, the declarative base is no longer an extension. Importing it from sqlalchemy.ext.declarative is deprecated and will be removed in SQLAlchemy 2.0.
Previously, the username was ignored from the URI. Starting from Redis>=6.0, that shouldn’t be the case since ACL support has landed.
Please refer to the documentation for details.
SQS now supports managed visibility timeout. This lets us implement a back off policy (for instance, an exponential policy) which means that the time between task failures will dynamically change based on the number of retries.
The trace function fetches the metadata from the backend each time it receives a task and compares its state. If the state is SUCCESS, we log and bail instead of executing the task. The task is acknowledged and everything proceeds normally.
Tasks with late acknowledgement keep running after restart, although the connection is lost and they cannot be acknowledged anymore. These tasks will now be terminated.
task.apply_async now supports passing ignore_result which will act the same
cached_property is heavily used in celery but it is causing issues in multi-threaded code since it is not thread safe. Celery is now using a thread-safe implementation of cached_property.
Tasks can now be defined like this:
from celery import shared_task @shared_task def my_func(*, name='default', age, city='Kyiv'): pass
The STS token requires a refresh after a certain period of time. After sts_token_timeout is reached, a new token will be created.
health_check_interval can be configured and will be passed to redis-py.
The pickle protocol version was updated to allow Celery to serialize larger strings among other benefits.