celery/docs/configuration.rst

.. _configuration:

============================
 Configuration and defaults
============================

This document describes the configuration options available.

If you're using the default loader, you must create the :file:`celeryconfig.py`
module and make sure it is available on the Python path.

.. contents::
    :local:
    :depth: 2

.. _conf-example:

Example configuration file
==========================

This is an example configuration file to get you started.
It should contain all you need to run a basic Celery set-up.

.. code-block:: python

    ## Broker settings.
    broker_url = 'amqp://guest:guest@localhost:5672//'

    # List of modules to import when celery starts.
    imports = ('myapp.tasks',)

    ## Using the database to store task state and results.
    result_backend = 'db+sqlite:///results.db'

    task_annotations = {'tasks.add': {'rate_limit': '10/s'}}

Configuration Directives
========================

.. _conf-datetime:

General settings
----------------

.. setting:: accept_content

accept_content
~~~~~~~~~~~~~~

A whitelist of content-types/serializers to allow.

If a message is received that is not in this list then
the message will be discarded with an error.

By default any content type is enabled (including pickle and yaml)
so make sure untrusted parties do not have access to your broker.
See :ref:`guide-security` for more.

Example::

    # using serializer name
    accept_content = ['json']

    # or the actual content-type (MIME)
    accept_content = ['application/json']

Time and date settings
----------------------

.. setting:: enable_utc

enable_utc
~~~~~~~~~~

.. versionadded:: 2.5

If enabled dates and times in messages will be converted to use
the UTC timezone.

Note that workers running Celery versions below 2.5 will assume a local
timezone for all messages, so only enable if all workers have been
upgraded.

Enabled by default since version 3.0.

.. setting:: timezone

timezone
~~~~~~~~

Configure Celery to use a custom time zone.
The timezone value can be any time zone supported by the `pytz`_
library.

If not set the UTC timezone is used.  For backwards compatibility
there is also a :setting:`enable_utc` setting, and this is set
to false the system local timezone is used instead.

.. _`pytz`: http://pypi.python.org/pypi/pytz/

.. _conf-tasks:

Task settings
-------------

.. setting:: task_annotations

task_annotations
~~~~~~~~~~~~~~~~

This setting can be used to rewrite any task attribute from the
configuration.  The setting can be a dict, or a list of annotation
objects that filter for tasks and return a map of attributes
to change.

This will change the ``rate_limit`` attribute for the ``tasks.add``
task:

.. code-block:: python

    task_annotations = {'tasks.add': {'rate_limit': '10/s'}}

or change the same for all tasks:

.. code-block:: python

    task_annotations = {'*': {'rate_limit': '10/s'}}

You can change methods too, for example the ``on_failure`` handler:

.. code-block:: python

    def my_on_failure(self, exc, task_id, args, kwargs, einfo):
        print('Oh no! Task failed: {0!r}'.format(exc))

    task_annotations = {'*': {'on_failure': my_on_failure}}

If you need more flexibility then you can use objects
instead of a dict to choose which tasks to annotate:

.. code-block:: python

    class MyAnnotate(object):

        def annotate(self, task):
            if task.name.startswith('tasks.'):
                return {'rate_limit': '10/s'}

    task_annotations = (MyAnnotate(), {…})

.. setting:: task_compression

task_compression
~~~~~~~~~~~~~~~~

Default compression used for task messages.
Can be ``gzip``, ``bzip2`` (if available), or any custom
compression schemes registered in the Kombu compression registry.

The default is to send uncompressed messages.

.. setting:: task_protocol

task_protocol
~~~~~~~~~~~~~

Default task message protocol version.
Supports protocols: 1 and 2 (default is 1 for backwards compatibility).

.. setting:: task_serializer

task_serializer
~~~~~~~~~~~~~~~

A string identifying the default serialization method to use.  Can be
`pickle` (default), `json`, `yaml`, `msgpack` or any custom serialization
methods that have been registered with :mod:`kombu.serialization.registry`.

.. seealso::

    :ref:`calling-serializers`.

.. setting:: task_publish_retry

task_publish_retry
~~~~~~~~~~~~~~~~~~

.. versionadded:: 2.2

Decides if publishing task messages will be retried in the case
of connection loss or other connection errors.
See also :setting:`task_publish_retry_policy`.

Enabled by default.

.. setting:: task_publish_retry_policy

task_publish_retry_policy
~~~~~~~~~~~~~~~~~~~~~~~~~

.. versionadded:: 2.2

Defines the default policy when retrying publishing a task message in
the case of connection loss or other connection errors.

See :ref:`calling-retry` for more information.
.. _conf-task-execution:

Task execution settings
-----------------------

.. setting:: task_always_eager

task_always_eager
~~~~~~~~~~~~~~~~~

If this is :const:`True`, all tasks will be executed locally by blocking until
the task returns.  ``apply_async()`` and ``Task.delay()`` will return
an :class:`~celery.result.EagerResult` instance, which emulates the API
and behavior of :class:`~celery.result.AsyncResult`, except the result
is already evaluated.

That is, tasks will be executed locally instead of being sent to
the queue.

.. setting:: task_eager_propagates_exceptions

task_eager_propagates_exceptions
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

If this is :const:`True`, eagerly executed tasks (applied by `task.apply()`,
or when the :setting:`task_always_eager` setting is enabled), will
propagate exceptions.

It's the same as always running ``apply()`` with ``throw=True``.

.. setting:: task_ignore_result

task_ignore_result
~~~~~~~~~~~~~~~~~~

Whether to store the task return values or not (tombstones).
If you still want to store errors, just not successful return values,
you can set :setting:`task_store_errors_even_if_ignored`.

.. setting:: task_store_errors_even_if_ignored

task_store_errors_even_if_ignored
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

If set, the worker stores all task errors in the result store even if
:attr:`Task.ignore_result <celery.task.base.Task.ignore_result>` is on.

.. setting:: task_track_started

task_track_started
~~~~~~~~~~~~~~~~~~

If :const:`True` the task will report its status as "started" when the
task is executed by a worker.  The default value is :const:`False` as
the normal behaviour is to not report that level of granularity.  Tasks
are either pending, finished, or waiting to be retried.  Having a "started"
state can be useful for when there are long running tasks and there is a
need to report which task is currently running.

.. setting:: task_time_limit

task_time_limit
~~~~~~~~~~~~~~~

Task hard time limit in seconds.  The worker processing the task will
be killed and replaced with a new one when this is exceeded.

.. setting:: task_soft_time_limit

task_soft_time_limit
~~~~~~~~~~~~~~~~~~~~

Task soft time limit in seconds.

The :exc:`~@SoftTimeLimitExceeded` exception will be
raised when this is exceeded.  The task can catch this to
e.g. clean up before the hard time limit comes.

Example:

.. code-block:: python

    from celery.exceptions import SoftTimeLimitExceeded

    @app.task
    def mytask():
        try:
            return do_work()
        except SoftTimeLimitExceeded:
            cleanup_in_a_hurry()

.. setting:: task_acks_late

task_acks_late
~~~~~~~~~~~~~~

Late ack means the task messages will be acknowledged **after** the task
has been executed, not *just before*, which is the default behavior.

.. seealso::

    FAQ: :ref:`faq-acks_late-vs-retry`.

.. setting:: task_reject_on_worker_lost

task_reject_on_worker_lost
~~~~~~~~~~~~~~~~~~~~~~~~~~

Even if :setting:`task_acks_late` is enabled, the worker will
acknowledge tasks when the worker process executing them abrubtly
exits or is signalled (e.g. :sig:`KILL`/:sig:`INT`, etc).

Setting this to true allows the message to be requeued instead,
so that the task will execute again by the same worker, or another
worker.

.. warning::

    Enabling this can cause message loops; make sure you know
    what you're doing.

.. setting:: task_default_rate_limit

task_default_rate_limit
~~~~~~~~~~~~~~~~~~~~~~~

The global default rate limit for tasks.

This value is used for tasks that does not have a custom rate limit
The default is no rate limit.

.. seealso::

    The setting:`worker_disable_rate_limits` setting can
    disable all rate limits.

.. _conf-result-backend:

Task result backend settings
----------------------------

.. setting:: result_backend

result_backend
~~~~~~~~~~~~~~

The backend used to store task results (tombstones).
Disabled by default.
Can be one of the following:

* rpc
    Send results back as AMQP messages
    See :ref:`conf-rpc-result-backend`.

* database
    Use a relational database supported by `SQLAlchemy`_.
    See :ref:`conf-database-result-backend`.

* redis
    Use `Redis`_ to store the results.
    See :ref:`conf-redis-result-backend`.

* cache
    Use `memcached`_ to store the results.
    See :ref:`conf-cache-result-backend`.

* mongodb
    Use `MongoDB`_ to store the results.
    See :ref:`conf-mongodb-result-backend`.

* new_cassandra
    Use `Cassandra`_ to store the results, using newer database driver than _cassandra_.
    See :ref:`conf-new_cassandra-result-backend`.

* ironcache
    Use `IronCache`_ to store the results.
    See :ref:`conf-ironcache-result-backend`.

* couchbase
    Use `Couchbase`_ to store the results.
    See :ref:`conf-couchbase-result-backend`.

* couchdb
    Use `CouchDB`_ to store the results.
    See :ref:`conf-couchdb-result-backend`.

* amqp
    Older AMQP backend (badly) emulating a database-based backend.
    See :ref:`conf-amqp-result-backend`.

.. warning:

    While the AMQP result backend is very efficient, you must make sure
    you only receive the same result once.  See :doc:`userguide/calling`).

.. _`SQLAlchemy`: http://sqlalchemy.org
.. _`memcached`: http://memcached.org
.. _`MongoDB`: http://mongodb.org
.. _`Redis`: http://redis.io
.. _`Cassandra`: http://cassandra.apache.org/
.. _`IronCache`: http://www.iron.io/cache
.. _`CouchDB`: http://www.couchdb.com/
.. _`Couchbase`: http://www.couchbase.com/

.. setting:: result_serializer

result_serializer
~~~~~~~~~~~~~~~~~

Result serialization format.  Default is ``pickle``. See
:ref:`calling-serializers` for information about supported
serialization formats.

.. setting:: result_compression

result_compression
~~~~~~~~~~~~~~~~~~

Optional compression method used for task results.
Supports the same options as the :setting:`task_serializer` setting.

Default is no compression.

.. setting:: result_expires

result_expires
~~~~~~~~~~~~~~

Time (in seconds, or a :class:`~datetime.timedelta` object) for when after
stored task tombstones will be deleted.

A built-in periodic task will delete the results after this time
(``celery.backend_cleanup``), assuming that ``celery beat`` is
enabled.  The task runs daily at 4am.

A value of :const:`None` or 0 means results will never expire (depending
on backend specifications).

Default is to expire after 1 day.

.. note::

    For the moment this only works with the amqp, database, cache, redis and MongoDB
    backends.

    When using the database or MongoDB backends, `celery beat` must be
    running for the results to be expired.

.. setting:: result_cache_max

result_cache_max
~~~~~~~~~~~~~~~~

Result backends caches ready results used by the client.

This is the total number of results to cache before older results are evicted.
The default is 5000.  0 or None means no limit, and a value of :const:`-1`
will disable the cache.

.. _conf-database-result-backend:

Database backend settings
-------------------------

Database URL Examples
~~~~~~~~~~~~~~~~~~~~~

To use the database backend you have to configure the
:setting:`result_backend` setting with a connection URL and the ``db+``
prefix:

.. code-block:: python

    result_backend = 'db+scheme://user:password@host:port/dbname'

Examples::

    # sqlite (filename)
    result_backend = 'db+sqlite:///results.sqlite'

    # mysql
    result_backend = 'db+mysql://scott:tiger@localhost/foo'

    # postgresql
    result_backend = 'db+postgresql://scott:tiger@localhost/mydatabase'

    # oracle
    result_backend = 'db+oracle://scott:tiger@127.0.0.1:1521/sidname'

.. code-block:: python

Please see `Supported Databases`_ for a table of supported databases,
and `Connection String`_ for more information about connection
strings (which is the part of the URI that comes after the ``db+`` prefix).

.. _`Supported Databases`:
    http://www.sqlalchemy.org/docs/core/engines.html#supported-databases

.. _`Connection String`:
    http://www.sqlalchemy.org/docs/core/engines.html#database-urls

.. setting:: sqlalchemy_dburi

sqlalchemy_dburi
~~~~~~~~~~~~~~~~

This setting is no longer used as it's now possible to specify
the database URL directly in the :setting:`result_backend` setting.

.. setting:: sqlalchemy_engine_options

sqlalchemy_engine_options
~~~~~~~~~~~~~~~~~~~~~~~~~

To specify additional SQLAlchemy database engine options you can use
the :setting:`sqlalchmey_engine_options` setting::

    # echo enables verbose logging from SQLAlchemy.
    sqlalchemy_engine_options = {'echo': True}

.. setting:: sqlalchemy_short_lived_sessions

sqlalchemy_short_lived_sessions
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    sqlalchemy_short_lived_sessions = True

Short lived sessions are disabled by default.  If enabled they can drastically reduce
performance, especially on systems processing lots of tasks.  This option is useful
on low-traffic workers that experience errors as a result of cached database connections
going stale through inactivity.  For example, intermittent errors like
`(OperationalError) (2006, 'MySQL server has gone away')` can be fixed by enabling
short lived sessions.  This option only affects the database backend.

.. setting:: sqlalchemy_table_names

sqlalchemy_table_names
~~~~~~~~~~~~~~~~~~~~~~

When SQLAlchemy is configured as the result backend, Celery automatically
creates two tables to store result metadata for tasks.  This setting allows
you to customize the table names:

.. code-block:: python

    # use custom table names for the database result backend.
    sqlalchemy_table_names = {
        'task': 'myapp_taskmeta',
        'group': 'myapp_groupmeta',
    }

.. _conf-rpc-result-backend:

RPC backend settings
--------------------

.. setting:: result_persistent

result_persistent
~~~~~~~~~~~~~~~~~

If set to :const:`True`, result messages will be persistent.  This means the
messages will not be lost after a broker restart.  The default is for the
results to be transient.

Example configuration
~~~~~~~~~~~~~~~~~~~~~

.. code-block:: python

    result_backend = 'rpc://'
    result_persistent = False

.. _conf-cache-result-backend:

Cache backend settings
----------------------

.. note::

    The cache backend supports the `pylibmc`_ and `python-memcached`
    libraries.  The latter is used only if `pylibmc`_ is not installed.

Using a single memcached server:

.. code-block:: python

    result_backend = 'cache+memcached://127.0.0.1:11211/'

Using multiple memcached servers:

.. code-block:: python

    result_backend = """
        cache+memcached://172.19.26.240:11211;172.19.26.242:11211/
    """.strip()

The "memory" backend stores the cache in memory only:

.. code-block:: python

    result_backend = 'cache'
    cache_backend = 'memory'

.. setting:: cache_backend_options

cache_backend_options
~~~~~~~~~~~~~~~~~~~~~

You can set pylibmc options using the :setting:`cache_backend_options`
setting:

.. code-block:: python

    cache_backend_options = {
        'binary': True,
        'behaviors': {'tcp_nodelay': True},
    }

.. _`pylibmc`: http://sendapatch.se/projects/pylibmc/

.. setting:: cache_backend

cache_backend
~~~~~~~~~~~~~

This setting is no longer used as it's now possible to specify
the cache backend directly in the :setting:`result_backend` setting.

.. _conf-redis-result-backend:

Redis backend settings
----------------------

Configuring the backend URL
~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. note::

    The Redis backend requires the :mod:`redis` library:
    http://pypi.python.org/pypi/redis/

    To install the redis package use `pip` or `easy_install`:

    .. code-block:: console

        $ pip install redis

This backend requires the :setting:`result_backend`
setting to be set to a Redis URL::

    result_backend = 'redis://:password@host:port/db'

For example::

    result_backend = 'redis://localhost/0'

which is the same as::

    result_backend = 'redis://'

The fields of the URL are defined as follows:

- *host*

Host name or IP address of the Redis server. e.g. `localhost`.

- *port*

Port to the Redis server. Default is 6379.

- *db*

Database number to use. Default is 0.
The db can include an optional leading slash.

- *password*

Password used to connect to the database.

.. setting:: redis_max_connections

redis_max_connections
~~~~~~~~~~~~~~~~~~~~~

Maximum number of connections available in the Redis connection
pool used for sending and retrieving results.

.. _conf-mongodb-result-backend:

MongoDB backend settings
------------------------

.. note::

    The MongoDB backend requires the :mod:`pymongo` library:
    http://github.com/mongodb/mongo-python-driver/tree/master

.. setting:: mongodb_backend_settings

mongodb_backend_settings
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This is a dict supporting the following keys:

* database
    The database name to connect to. Defaults to ``celery``.

* taskmeta_collection
    The collection name to store task meta data.
    Defaults to ``celery_taskmeta``.

* max_pool_size
    Passed as max_pool_size to PyMongo's Connection or MongoClient
    constructor. It is the maximum number of TCP connections to keep
    open to MongoDB at a given time. If there are more open connections
    than max_pool_size, sockets will be closed when they are released.
    Defaults to 10.

* options

    Additional keyword arguments to pass to the mongodb connection
    constructor.  See the :mod:`pymongo` docs to see a list of arguments
    supported.

.. _example-mongodb-result-config:

Example configuration
~~~~~~~~~~~~~~~~~~~~~

.. code-block:: python

    result_backend = 'mongodb://192.168.1.100:30000/'
    mongodb_backend_settings = {
        'database': 'mydb',
        'taskmeta_collection': 'my_taskmeta_collection',
    }

.. _conf-new_cassandra-result-backend:

new_cassandra backend settings
------------------------------

.. note::

    This Cassandra backend driver requires :mod:`cassandra-driver`.
    https://pypi.python.org/pypi/cassandra-driver

    To install, use `pip` or `easy_install`:

    .. code-block:: bash

        $ pip install cassandra-driver

This backend requires the following configuration directives to be set.

.. setting:: cassandra_servers

cassandra_servers
~~~~~~~~~~~~~~~~~

List of ``host`` Cassandra servers. e.g.::

    cassandra_servers = ['localhost']


.. setting:: cassandra_port

cassandra_port
~~~~~~~~~~~~~~

Port to contact the Cassandra servers on. Default is 9042.

.. setting:: cassandra_keyspace

cassandra_keyspace
~~~~~~~~~~~~~~~~~~

The keyspace in which to store the results. e.g.::

    cassandra_keyspace = 'tasks_keyspace'

.. setting:: cassandra_column_family

cassandra_column_family
~~~~~~~~~~~~~~~~~~~~~~~

The table (column family) in which to store the results. e.g.::

    cassandra_column_family = 'tasks'

.. setting:: cassandra_read_consistency

cassandra_read_consistency
~~~~~~~~~~~~~~~~~~~~~~~~~~

The read consistency used. Values can be ``ONE``, ``TWO``, ``THREE``, ``QUORUM``, ``ALL``,
``LOCAL_QUORUM``, ``EACH_QUORUM``, ``LOCAL_ONE``.

.. setting:: cassandra_write_consistency

cassandra_write_consistency
~~~~~~~~~~~~~~~~~~~~~~~~~~~

The write consistency used. Values can be ``ONE``, ``TWO``, ``THREE``, ``QUORUM``, ``ALL``,
``LOCAL_QUORUM``, ``EACH_QUORUM``, ``LOCAL_ONE``.

.. setting:: cassandra_entry_ttl

cassandra_entry_ttl
~~~~~~~~~~~~~~~~~~~

Time-to-live for status entries. They will expire and be removed after that many seconds
after adding. Default (None) means they will never expire.

Example configuration
~~~~~~~~~~~~~~~~~~~~~

.. code-block:: python

    cassandra_servers = ['localhost']
    cassandra_keyspace = 'celery'
    cassandra_column_family = 'task_results'
    cassandra_read_consistency = 'ONE'
    cassandra_write_consistency = 'ONE'
    cassandra_entry_ttl = 86400

.. _conf-riak-result-backend:

Riak backend settings
---------------------

.. note::

    The Riak backend requires the :mod:`riak` library:
    http://pypi.python.org/pypi/riak/

    To install the riak package use `pip` or `easy_install`:

    .. code-block:: console

        $ pip install riak

This backend requires the :setting:`result_backend`
setting to be set to a Riak URL::

    result_backend = "riak://host:port/bucket"

For example::

    result_backend = "riak://localhost/celery

which is the same as::

    result_backend = "riak://"

The fields of the URL are defined as follows:

- *host*

Host name or IP address of the Riak server. e.g. `"localhost"`.

- *port*

Port to the Riak server using the protobuf protocol. Default is 8087.

- *bucket*

Bucket name to use. Default is `celery`.
The bucket needs to be a string with ascii characters only.

Altenatively, this backend can be configured with the following configuration directives.

.. setting:: riak_backend_settings

riak_backend_settings
~~~~~~~~~~~~~~~~~~~~~

This is a dict supporting the following keys:

* host
    The host name of the Riak server. Defaults to "localhost".

* port
    The port the Riak server is listening to. Defaults to 8087.

* bucket
    The bucket name to connect to. Defaults to "celery".

* protocol
    The protocol to use to connect to the Riak server. This is not configurable
    via :setting:`result_backend`

.. _conf-ironcache-result-backend:

IronCache backend settings
--------------------------

.. note::

    The IronCache backend requires the :mod:`iron_celery` library:
    http://pypi.python.org/pypi/iron_celery

    To install the iron_celery package use `pip` or `easy_install`:

    .. code-block:: console

        $ pip install iron_celery

IronCache is configured via the URL provided in :setting:`result_backend`, for example::

    result_backend = 'ironcache://project_id:token@'

Or to change the cache name::

    ironcache:://project_id:token@/awesomecache

For more information, see: https://github.com/iron-io/iron_celery

.. _conf-couchbase-result-backend:

Couchbase backend settings
--------------------------

.. note::

    The Couchbase backend requires the :mod:`couchbase` library:
    https://pypi.python.org/pypi/couchbase

    To install the couchbase package use `pip` or `easy_install`:

    .. code-block:: console

        $ pip install couchbase

This backend can be configured via the :setting:`result_backend`
set to a couchbase URL::

    result_backend = 'couchbase://username:password@host:port/bucket'

.. setting:: couchbase_backend_settings

couchbase_backend_settings
~~~~~~~~~~~~~~~~~~~~~~~~~~

This is a dict supporting the following keys:

* host
    Host name of the Couchbase server. Defaults to ``localhost``.

* port
    The port the Couchbase server is listening to. Defaults to ``8091``.

* bucket
    The default bucket the Couchbase server is writing to.
    Defaults to ``default``.

* username
    User name to authenticate to the Couchbase server as (optional).

* password
    Password to authenticate to the Couchbase server (optional).

.. _conf-couchdb-result-backend:

CouchDB backend settings
------------------------

.. note::

    The CouchDB backend requires the :mod:`pycouchdb` library:
    https://pypi.python.org/pypi/pycouchdb

    To install the couchbase package use `pip` or `easy_install`:

    .. code-block:: console

        $ pip install pycouchdb

This backend can be configured via the :setting:`result_backend`
set to a couchdb URL::

    result_backend = 'couchdb://username:password@host:port/container'

The URL is formed out of the following parts:

* username
    User name to authenticate to the CouchDB server as (optional).

* password
    Password to authenticate to the CouchDB server (optional).

* host
    Host name of the CouchDB server. Defaults to ``localhost``.

* port
    The port the CouchDB server is listening to. Defaults to ``8091``.

* container
    The default container the CouchDB server is writing to.
    Defaults to ``default``.

.. _conf-amqp-result-backend:

AMQP backend settings
---------------------

.. admonition:: Do not use in production.

    This is the old AMQP result backend that creates one queue per task,
    if you want to send results back as message please consider using the
    RPC backend instead, or if you need the results to be persistent
    use a result backend designed for that purpose (e.g. Redis, or a database).

.. note::

    The AMQP backend requires RabbitMQ 1.1.0 or higher to automatically
    expire results.  If you are running an older version of RabbitMQ
    you should disable result expiration like this:

        result_expires = None

.. setting:: result_exchange

result_exchange
~~~~~~~~~~~~~~~

Name of the exchange to publish results in.  Default is `celeryresults`.

.. setting:: result_exchange_type

result_exchange_type
~~~~~~~~~~~~~~~~~~~~

The exchange type of the result exchange.  Default is to use a `direct`
exchange.

result_persistent
~~~~~~~~~~~~~~~~~

If set to :const:`True`, result messages will be persistent.  This means the
messages will not be lost after a broker restart.  The default is for the
results to be transient.

Example configuration
~~~~~~~~~~~~~~~~~~~~~

.. code-block:: python

    result_backend = 'amqp'
    result_expires = 18000  # 5 hours.

.. _conf-messaging:

Message Routing
---------------

.. _conf-messaging-routing:

.. setting:: task_queues

task_queues
~~~~~~~~~~~

Most users will not want to specify this setting and should rather use
the :ref:`automatic routing facilities <routing-automatic>`.

If you really want to configure advanced routing, this setting should
be a list of :class:`kombu.Queue` objects the worker will consume from.

Note that workers can be overriden this setting via the `-Q` option,
or individual queues from this list (by name) can be excluded using
the `-X` option.

Also see :ref:`routing-basics` for more information.

The default is a queue/exchange/binding key of ``celery``, with
exchange type ``direct``.

See also :setting:`task_routes`

.. setting:: task_routes

task_routes
~~~~~~~~~~~~~

A list of routers, or a single router used to route tasks to queues.
When deciding the final destination of a task the routers are consulted
in order.

A router can be specified as either:

*  A router class instances
*  A string which provides the path to a router class
*  A dict containing router specification. It will be converted to a :class:`celery.routes.MapRoute` instance.

Examples:

.. code-block:: python

    task_routes = {
        "celery.ping": "default",
        "mytasks.add": "cpu-bound",
        "video.encode": {
            "queue": "video",
            "exchange": "media"
            "routing_key": "media.video.encode",
        },
    }

    task_routes = ("myapp.tasks.Router", {"celery.ping": "default})

Where ``myapp.tasks.Router`` could be:

.. code-block:: python

    class Router(object):

        def route_for_task(self, task, args=None, kwargs=None):
            if task == "celery.ping":
                return "default"

``route_for_task`` may return a string or a dict. A string then means
it's a queue name in :setting:`task_queues`, a dict means it's a custom route.

When sending tasks, the routers are consulted in order. The first
router that doesn't return ``None`` is the route to use. The message options
is then merged with the found route settings, where the routers settings
have priority.

Example if :func:`~celery.execute.apply_async` has these arguments:

.. code-block:: python

   Task.apply_async(immediate=False, exchange="video",
                    routing_key="video.compress")

and a router returns:

.. code-block:: python

    {"immediate": True, "exchange": "urgent"}

the final message options will be:

.. code-block:: python

    immediate=True, exchange="urgent", routing_key="video.compress"

(and any default message options defined in the
:class:`~celery.task.base.Task` class)

Values defined in :setting:`task_routes` have precedence over values defined in
:setting:`task_queues` when merging the two.

With the follow settings:

.. code-block:: python

    task_queues = {
        "cpubound": {
            "exchange": "cpubound",
            "routing_key": "cpubound",
        },
    }

    task_routes = {
        "tasks.add": {
            "queue": "cpubound",
            "routing_key": "tasks.add",
            "serializer": "json",
        },
    }

The final routing options for ``tasks.add`` will become:

.. code-block:: javascript

    {"exchange": "cpubound",
     "routing_key": "tasks.add",
     "serializer": "json"}

See :ref:`routers` for more examples.

.. setting:: task_queue_ha_policy

task_queue_ha_policy
~~~~~~~~~~~~~~~~~~~~
:brokers: RabbitMQ

This will set the default HA policy for a queue, and the value
can either be a string (usually ``all``):

.. code-block:: python

    task_queue_ha_policy = 'all'

Using 'all' will replicate the queue to all current nodes,
Or you can give it a list of nodes to replicate to:

.. code-block:: python

    task_queue_ha_policy = ['rabbit@host1', 'rabbit@host2']

Using a list will implicitly set ``x-ha-policy`` to 'nodes' and
``x-ha-policy-params`` to the given list of nodes.

See http://www.rabbitmq.com/ha.html for more information.

.. setting:: worker_direct

worker_direct
~~~~~~~~~~~~~

This option enables so that every worker has a dedicated queue,
so that tasks can be routed to specific workers.

The queue name for each worker is automatically generated based on
the worker hostname and a ``.dq`` suffix, using the ``C.dq`` exchange.

For example the queue name for the worker with node name ``w1@example.com``
becomes::

    w1@example.com.dq

Then you can route the task to the task by specifying the hostname
as the routing key and the ``C.dq`` exchange::

    task_routes = {
        'tasks.add': {'exchange': 'C.dq', 'routing_key': 'w1@example.com'}
    }

.. setting:: task_create_missing_queues

task_create_missing_queues
~~~~~~~~~~~~~~~~~~~~~~~~~~

If enabled (default), any queues specified that are not defined in
:setting:`task_queues` will be automatically created. See
:ref:`routing-automatic`.

.. setting:: task_default_queue

task_default_queue
~~~~~~~~~~~~~~~~~~

The name of the default queue used by `.apply_async` if the message has
no route or no custom queue has been specified.

This queue must be listed in :setting:`task_queues`.
If :setting:`task_queues` is not specified then it is automatically
created containing one queue entry, where this name is used as the name of
that queue.

The default is: `celery`.

.. seealso::

    :ref:`routing-changing-default-queue`

.. setting:: task_default_exchange

task_default_exchange
~~~~~~~~~~~~~~~~~~~~~

Name of the default exchange to use when no custom exchange is
specified for a key in the :setting:`task_queues` setting.

The default is: `celery`.

.. setting:: task_default_exchange_type

task_default_exchange_type
~~~~~~~~~~~~~~~~~~~~~~~~~~

Default exchange type used when no custom exchange type is specified
for a key in the :setting:`task_queues` setting.
The default is: `direct`.

.. setting:: task_default_routing_key

task_default_routing_key
~~~~~~~~~~~~~~~~~~~~~~~~

The default routing key used when no custom routing key
is specified for a key in the :setting:`task_queues` setting.

The default is: `celery`.

.. setting:: task_default_delivery_mode

task_default_delivery_mode
~~~~~~~~~~~~~~~~~~~~~~~~~~

Can be `transient` or `persistent`.  The default is to send
persistent messages.

.. _conf-broker-settings:

Broker Settings
---------------

.. setting:: broker_url

broker_url
~~~~~~~~~~

Default broker URL.  This must be an URL in the form of::

    transport://userid:password@hostname:port/virtual_host

Only the scheme part (``transport://``) is required, the rest
is optional, and defaults to the specific transports default values.

The transport part is the broker implementation to use, and the
default is ``amqp``, which uses ``librabbitmq`` by default or falls back to
``pyamqp`` if that is not installed.  Also there are many other choices including
``redis``, ``beanstalk``, ``sqlalchemy``, ``django``, ``mongodb``,
``couchdb``.
It can also be a fully qualified path to your own transport implementation.

More than broker URL, of the same transport, can also be specified.
The broker URLs can be passed in as a single string that is semicolon delimited::

    broker_url = 'transport://userid:password@hostname:port//;transport://userid:password@hostname:port//'

Or as a list::

    broker_url = [
        'transport://userid:password@localhost:port//',
        'transport://userid:password@hostname:port//'
    ]

The brokers will then be used in the :setting:`broker_failover_strategy`.

See :ref:`kombu:connection-urls` in the Kombu documentation for more
information.

.. setting:: broker_failover_strategy

broker_failover_strategy
~~~~~~~~~~~~~~~~~~~~~~~~

Default failover strategy for the broker Connection object. If supplied,
may map to a key in 'kombu.connection.failover_strategies', or be a reference
to any method that yields a single item from a supplied list.

Example::

    # Random failover strategy
    def random_failover_strategy(servers):
        it = list(it)  # don't modify callers list
        shuffle = random.shuffle
        for _ in repeat(None):
            shuffle(it)
            yield it[0]

    broker_failover_strategy = random_failover_strategy

.. setting:: broker_heartbeat

broker_heartbeat
~~~~~~~~~~~~~~~~
:transports supported: ``pyamqp``

It's not always possible to detect connection loss in a timely
manner using TCP/IP alone, so AMQP defines something called heartbeats
that's is used both by the client and the broker to detect if
a connection was closed.

Heartbeats are disabled by default.

If the heartbeat value is 10 seconds, then
the heartbeat will be monitored at the interval specified
by the :setting:`broker_heartbeat_checkrate` setting, which by default is
double the rate of the heartbeat value
(so for the default 10 seconds, the heartbeat is checked every 5 seconds).

.. setting:: broker_heartbeat_checkrate

broker_heartbeat_checkrate
~~~~~~~~~~~~~~~~~~~~~~~~~~
:transports supported: ``pyamqp``

At intervals the worker will monitor that the broker has not missed
too many heartbeats.  The rate at which this is checked is calculated
by dividing the :setting:`broker_heartbeat` value with this value,
so if the heartbeat is 10.0 and the rate is the default 2.0, the check
will be performed every 5 seconds (twice the heartbeat sending rate).

.. setting:: broker_use_ssl

broker_use_ssl
~~~~~~~~~~~~~~
:transports supported: ``pyamqp``, ``redis``

Toggles SSL usage on broker connection and SSL settings.

If ``True`` the connection will use SSL with default SSL settings.
If set to a dict, will configure SSL connection according to the specified
policy. The format used is python `ssl.wrap_socket()
options <https://docs.python.org/3/library/ssl.html#ssl.wrap_socket>`_.

Default is ``False`` (no SSL).

Note that SSL socket is generally served on a separate port by the broker.

Example providing a client cert and validating the server cert against a custom
certificate authority:

.. code-block:: python

    import ssl

    broker_use_ssl = {
      'keyfile': '/var/ssl/private/worker-key.pem',
      'certfile': '/var/ssl/amqp-server-cert.pem',
      'ca_certs': '/var/ssl/myca.pem',
      'cert_reqs': ssl.CERT_REQUIRED
    }

.. warning::

    Be careful using ``broker_use_ssl=True``, it is possible that your default
    configuration do not validate the server cert at all, please read Python
    `ssl module security
    considerations <https://docs.python.org/3/library/ssl.html#ssl-security>`_.

.. setting:: broker_pool_limit

broker_pool_limit
~~~~~~~~~~~~~~~~~

.. versionadded:: 2.3

The maximum number of connections that can be open in the connection pool.

The pool is enabled by default since version 2.5, with a default limit of ten
connections.  This number can be tweaked depending on the number of
threads/greenthreads (eventlet/gevent) using a connection.  For example
running eventlet with 1000 greenlets that use a connection to the broker,
contention can arise and you should consider increasing the limit.

If set to :const:`None` or 0 the connection pool will be disabled and
connections will be established and closed for every use.

Default (since 2.5) is to use a pool of 10 connections.

.. setting:: broker_connection_timeout

broker_connection_timeout
~~~~~~~~~~~~~~~~~~~~~~~~~

The default timeout in seconds before we give up establishing a connection
to the AMQP server.  Default is 4 seconds.

.. setting:: broker_connection_retry

broker_connection_retry
~~~~~~~~~~~~~~~~~~~~~~~

Automatically try to re-establish the connection to the AMQP broker if lost.

The time between retries is increased for each retry, and is
not exhausted before :setting:`broker_connection_max_retries` is
exceeded.

This behavior is on by default.

.. setting:: broker_connection_max_retries

broker_connection_max_retries
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Maximum number of retries before we give up re-establishing a connection
to the AMQP broker.

If this is set to :const:`0` or :const:`None`, we will retry forever.

Default is 100 retries.

.. setting:: broker_login_method

broker_login_method
~~~~~~~~~~~~~~~~~~~

Set custom amqp login method, default is ``AMQPLAIN``.

.. setting:: broker_transport_options

broker_transport_options
~~~~~~~~~~~~~~~~~~~~~~~~

.. versionadded:: 2.2

A dict of additional options passed to the underlying transport.

See your transport user manual for supported options (if any).

Example setting the visibility timeout (supported by Redis and SQS
transports):

.. code-block:: python

    broker_transport_options = {'visibility_timeout': 18000}  # 5 hours

.. _conf-worker:

Worker
------

.. setting:: imports

imports
~~~~~~~

A sequence of modules to import when the worker starts.

This is used to specify the task modules to import, but also
to import signal handlers and additional remote control commands, etc.

The modules will be imported in the original order.

.. setting:: include

include
~~~~~~~

Exact same semantics as :setting:`imports`, but can be used as a means
to have different import categories.

The modules in this setting are imported after the modules in
:setting:`imports`.

.. _conf-concurrency:

.. setting:: worker_concurrency

worker_concurrency
~~~~~~~~~~~~~~~~~~

The number of concurrent worker processes/threads/green threads executing
tasks.

If you're doing mostly I/O you can have more processes,
but if mostly CPU-bound, try to keep it close to the
number of CPUs on your machine. If not set, the number of CPUs/cores
on the host will be used.

Defaults to the number of available CPUs.

.. setting:: worker_prefetch_multiplier

worker_prefetch_multiplier
~~~~~~~~~~~~~~~~~~~~~~~~~~

How many messages to prefetch at a time multiplied by the number of
concurrent processes.  The default is 4 (four messages for each
process).  The default setting is usually a good choice, however -- if you
have very long running tasks waiting in the queue and you have to start the
workers, note that the first worker to start will receive four times the
number of messages initially.  Thus the tasks may not be fairly distributed
to the workers.

To disable prefetching, set :setting:`worker_prefetch_multiplier` to 1.
Changing that setting to 0 will allow the worker to keep consuming
as many messages as it wants.

For more on prefetching, read :ref:`optimizing-prefetch-limit`

.. note::

    Tasks with ETA/countdown are not affected by prefetch limits.

.. setting:: worker_lost_wait

worker_lost_wait
~~~~~~~~~~~~~~~~

In some cases a worker may be killed without proper cleanup,
and the worker may have published a result before terminating.
This value specifies how long we wait for any missing results before
raising a :exc:`@WorkerLostError` exception.

Default is 10.0

.. setting:: worker_max_tasks_per_child

worker_max_tasks_per_child
~~~~~~~~~~~~~~~~~~~~~~~~~~~

Maximum number of tasks a pool worker process can execute before
it's replaced with a new one.  Default is no limit.

.. setting:: worker_max_memory_per_child

worker_max_memory_per_child
~~~~~~~~~~~~~~~~~~~~~~~~~~~

Maximum amount of resident memory that may be consumed by a
worker before it will be replaced by a new worker. If a single
task causes a worker to exceed this limit, the task will be
completed, and the worker will be replaced afterwards. Default:
no limit.

.. setting:: worker_disable_rate_limits

worker_disable_rate_limits
~~~~~~~~~~~~~~~~~~~~~~~~~~

Disable all rate limits, even if tasks has explicit rate limits set.

.. setting:: worker_state_db

worker_state_db
~~~~~~~~~~~~~~~

Name of the file used to stores persistent worker state (like revoked tasks).
Can be a relative or absolute path, but be aware that the suffix `.db`
may be appended to the file name (depending on Python version).

Can also be set via the :option:`--statedb` argument to
:mod:`~celery.bin.worker`.

Not enabled by default.

.. setting:: worker_timer_precision

worker_timer_precision
~~~~~~~~~~~~~~~~~~~~~~

Set the maximum time in seconds that the ETA scheduler can sleep between
rechecking the schedule.  Default is 1 second.

Setting this value to 1 second means the schedulers precision will
be 1 second. If you need near millisecond precision you can set this to 0.1.

.. setting:: worker_enable_remote_control

worker_enable_remote_control
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Specify if remote control of the workers is enabled.

Default is :const:`True`.

.. _conf-error-mails:

Error E-Mails
-------------

.. setting:: task_send_error_emails

task_send_error_emails
~~~~~~~~~~~~~~~~~~~~~~

The default value for the `Task.send_error_emails` attribute, which if
set to :const:`True` means errors occurring during task execution will be
sent to :setting:`admins` by email.

Disabled by default.

.. setting:: admins

admins
~~~~~~

List of `(name, email_address)` tuples for the administrators that should
receive error emails.

.. setting:: server_email

server_email
~~~~~~~~~~~~

The email address this worker sends emails from.
Default is celery@localhost.

.. setting:: email_host

email_host
~~~~~~~~~~

The mail server to use.  Default is ``localhost``.

.. setting:: email_host_user

email_host_user
~~~~~~~~~~~~~~~

User name (if required) to log on to the mail server with.

.. setting:: email_host_password

email_host_password
~~~~~~~~~~~~~~~~~~~

Password (if required) to log on to the mail server with.

.. setting:: email_port

email_port
~~~~~~~~~~

The port the mail server is listening on.  Default is `25`.

.. setting:: email_use_ssl

email_use_ssl
~~~~~~~~~~~~~

Use SSL when connecting to the SMTP server.  Disabled by default.

.. setting:: email_use_tls

email_use_tls
~~~~~~~~~~~~~

Use TLS when connecting to the SMTP server.  Disabled by default.

.. setting:: email_timeout

email_timeout
~~~~~~~~~~~~~

Timeout in seconds for when we give up trying to connect
to the SMTP server when sending emails.

The default is 2 seconds.

.. setting:: email_charset

email_charset
~~~~~~~~~~~~~
.. versionadded:: 4.0

Charset for outgoing emails. Default is "us-ascii".

.. _conf-example-error-mail-config:

Example E-Mail configuration
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This configuration enables the sending of error emails to
george@vandelay.com and kramer@vandelay.com:

.. code-block:: python

    # Enables error emails.
    task_send_error_emails = True

    # Name and email addresses of recipients
    admins = (
        ('George Costanza', 'george@vandelay.com'),
        ('Cosmo Kramer', 'kosmo@vandelay.com'),
    )

    # Email address used as sender (From field).
    server_email = 'no-reply@vandelay.com'

    # Mailserver configuration
    email_host = 'mail.vandelay.com'
    email_port = 25
    # email_host_user = 'servers'
    # email_host_password = 's3cr3t'

.. _conf-events:

Events
------

.. setting:: worker_send_events

worker_send_events
~~~~~~~~~~~~~~~~~~

Send task-related events so that tasks can be monitored using tools like
`flower`.  Sets the default value for the workers :option:`-E` argument.

.. setting:: task_send_sent_event

task_send_sent_event
~~~~~~~~~~~~~~~~~~~~

.. versionadded:: 2.2

If enabled, a :event:`task-sent` event will be sent for every task so tasks can be
tracked before they are consumed by a worker.

Disabled by default.

.. setting:: event_queue_ttl

event_queue_ttl
~~~~~~~~~~~~~~~~~~~~~~
:transports supported: ``amqp``

Message expiry time in seconds (int/float) for when messages sent to a monitor clients
event queue is deleted (``x-message-ttl``)

For example, if this value is set to 10 then a message delivered to this queue
will be deleted after 10 seconds.

Disabled by default.

.. setting:: event_queue_expires

event_queue_expires
~~~~~~~~~~~~~~~~~~~
:transports supported: ``amqp``

Expiry time in seconds (int/float) for when after a monitor clients
event queue will be deleted (``x-expires``).

Default is never, relying on the queue autodelete setting.

.. setting:: event_serializer

event_serializer
~~~~~~~~~~~~~~~~

Message serialization format used when sending event messages.
Default is ``json``. See :ref:`calling-serializers`.

.. _conf-logging:

Logging
-------

.. setting:: worker_hijack_root_logger

worker_hijack_root_logger
~~~~~~~~~~~~~~~~~~~~~~~~~

.. versionadded:: 2.2

By default any previously configured handlers on the root logger will be
removed. If you want to customize your own logging handlers, then you
can disable this behavior by setting
`worker_hijack_root_logger = False`.

.. note::

    Logging can also be customized by connecting to the
    :signal:`celery.signals.setup_logging` signal.

.. setting:: worker_log_color

worker_log_color
~~~~~~~~~~~~~~~~~

Enables/disables colors in logging output by the Celery apps.

By default colors are enabled if

    1) the app is logging to a real terminal, and not a file.
    2) the app is not running on Windows.

.. setting:: worker_log_format

worker_log_format
~~~~~~~~~~~~~~~~~

The format to use for log messages.

Default is `[%(asctime)s: %(levelname)s/%(processName)s] %(message)s`

See the Python :mod:`logging` module for more information about log
formats.

.. setting:: worker_task_log_format

worker_task_log_format
~~~~~~~~~~~~~~~~~~~~~~

The format to use for log messages logged in tasks.  Can be overridden using
the :option:`--loglevel` option to :mod:`~celery.bin.worker`.

Default is::

    [%(asctime)s: %(levelname)s/%(processName)s]
        [%(task_name)s(%(task_id)s)] %(message)s

See the Python :mod:`logging` module for more information about log
formats.

.. setting:: worker_redirect_stdouts

worker_redirect_stdouts
~~~~~~~~~~~~~~~~~~~~~~~

If enabled `stdout` and `stderr` will be redirected
to the current logger.

Enabled by default.
Used by :program:`celery worker` and :program:`celery beat`.

.. setting:: worker_redirect_stdouts_level

worker_redirect_stdouts_level
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The log level output to `stdout` and `stderr` is logged as.
Can be one of :const:`DEBUG`, :const:`INFO`, :const:`WARNING`,
:const:`ERROR` or :const:`CRITICAL`.

Default is :const:`WARNING`.

.. _conf-security:

Security
--------

.. setting:: security_key

security_key
~~~~~~~~~~~~

.. versionadded:: 2.5

The relative or absolute path to a file containing the private key
used to sign messages when :ref:`message-signing` is used.

.. setting:: security_certificate

security_certificate
~~~~~~~~~~~~~~~~~~~~

.. versionadded:: 2.5

The relative or absolute path to an X.509 certificate file
used to sign messages when :ref:`message-signing` is used.

.. setting:: security_cert_store

security_cert_store
~~~~~~~~~~~~~~~~~~~

.. versionadded:: 2.5

The directory containing X.509 certificates used for
:ref:`message-signing`.  Can be a glob with wildcards,
(for example :file:`/etc/certs/*.pem`).

.. _conf-custom-components:

Custom Component Classes (advanced)
-----------------------------------

.. setting:: worker_pool

worker_pool
~~~~~~~~~~~

Name of the pool class used by the worker.

.. admonition:: Eventlet/Gevent

    Never use this option to select the eventlet or gevent pool.
    You must use the `-P` option instead, otherwise the monkey patching
    will happen too late and things will break in strange and silent ways.

Default is ``celery.concurrency.prefork:TaskPool``.

.. setting:: worker_pool_restarts

worker_pool_restarts
~~~~~~~~~~~~~~~~~~~~

If enabled the worker pool can be restarted using the
:control:`pool_restart` remote control command.

Disabled by default.

.. setting:: worker_autoscaler

worker_autoscaler
~~~~~~~~~~~~~~~~~

.. versionadded:: 2.2

Name of the autoscaler class to use.

Default is ``celery.worker.autoscale:Autoscaler``.

.. setting:: worker_autoreloader

worker_autoreloader
~~~~~~~~~~~~~~~~~~~

Name of the autoreloader class used by the worker to reload
Python modules and files that have changed.

Default is: ``celery.worker.autoreload:Autoreloader``.

.. setting:: worker_consumer

worker_consumer
~~~~~~~~~~~~~~~

Name of the consumer class used by the worker.
Default is :class:`celery.worker.consumer.Consumer`

.. setting:: worker_timer

worker_timer
~~~~~~~~~~~~

Name of the ETA scheduler class used by the worker.
Default is :class:`kombu.async.hub.timer.Timer`, or one overrided
by the pool implementation.

.. _conf-celerybeat:

Beat Settings (:program:`celery beat`)
--------------------------------------

.. setting:: beat_schedule

beat_schedule
~~~~~~~~~~~~~

The periodic task schedule used by :mod:`~celery.bin.beat`.
See :ref:`beat-entries`.

.. setting:: beat_scheduler

beat_scheduler
~~~~~~~~~~~~~~

The default scheduler class.  Default is ``celery.beat:PersistentScheduler``.

Can also be set via the :option:`-S` argument to
:mod:`~celery.bin.beat`.

.. setting:: beat_schedule_filename

beat_schedule_filename
~~~~~~~~~~~~~~~~~~~~~~

Name of the file used by `PersistentScheduler` to store the last run times
of periodic tasks.  Can be a relative or absolute path, but be aware that the
suffix `.db` may be appended to the file name (depending on Python version).

Can also be set via the :option:`--schedule` argument to
:mod:`~celery.bin.beat`.

.. setting:: beat_sync_every

beat_sync_every
~~~~~~~~~~~~~~~

The number of periodic tasks that can be called before another database sync
is issued.
Defaults to 0 (sync based on timing - default of 3 minutes as determined by
scheduler.sync_every). If set to 1, beat will call sync after every task
message sent.

.. setting:: beat_max_loop_interval

beat_max_loop_interval
~~~~~~~~~~~~~~~~~~~~~~

The maximum number of seconds :mod:`~celery.bin.beat` can sleep
between checking the schedule.

The default for this value is scheduler specific.
For the default celery beat scheduler the value is 300 (5 minutes),
but for e.g. the django-celery database scheduler it is 5 seconds
because the schedule may be changed externally, and so it must take
changes to the schedule into account.

Also when running celery beat embedded (:option:`-B`) on Jython as a thread
the max interval is overridden and set to 1 so that it's possible
to shut down in a timely manner.