This document describes the current stable version of Celery (3.1). For development docs, go here.

Configuration and defaults

This document describes the configuration options available.

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

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.

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

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

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

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

Configuration Directives

Time and date settings

CELERY_ENABLE_UTC

New in version 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.

CELERY_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 CELERY_ENABLE_UTC setting, and this is set to false the system local timezone is used instead.

Task settings

CELERY_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:

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

or change the same for all tasks:

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

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

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

CELERY_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:

class MyAnnotate(object):

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

CELERY_ANNOTATIONS = (MyAnnotate(), {…})

Concurrency settings

CELERYD_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.

CELERYD_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 CELERYD_PREFETCH_MULTIPLIER to 1. Setting CELERYD_PREFETCH_MULTIPLIER to 0 will allow the worker to keep consuming as many messages as it wants.

For more on prefetching, read Prefetch Limits

Note

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

Task result backend settings

CELERY_RESULT_BACKEND

Deprecated aliases:
 CELERY_BACKEND

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

CELERY_RESULT_SERIALIZER

Result serialization format. Default is pickle. See Serializers for information about supported serialization formats.

Database backend settings

Database URL Examples

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

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

Examples:

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

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

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

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

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).

CELERY_RESULT_DBURI

This setting is no longer used as it’s now possible to specify the database URL directly in the CELERY_RESULT_BACKEND setting.

CELERY_RESULT_ENGINE_OPTIONS

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

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

Short lived sessions

CELERY_RESULT_DB_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.

Specifying 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:

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

RPC backend settings

CELERY_RESULT_PERSISTENT

If set to 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

CELERY_RESULT_BACKEND = 'rpc://'
CELERY_RESULT_PERSISTENT = False

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:

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

Using multiple memcached servers:

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

The “memory” backend stores the cache in memory only:

CELERY_RESULT_BACKEND = 'cache'
CELERY_CACHE_BACKEND = 'memory'

CELERY_CACHE_BACKEND_OPTIONS

You can set pylibmc options using the CELERY_CACHE_BACKEND_OPTIONS setting:

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

CELERY_CACHE_BACKEND

This setting is no longer used as it’s now possible to specify the cache backend directly in the CELERY_RESULT_BACKEND setting.

Redis backend settings

Configuring the backend URL

Note

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

To install the redis package use pip or easy_install:

$ pip install redis

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

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

For example:

CELERY_RESULT_BACKEND = 'redis://localhost/0'

which is the same as:

CELERY_RESULT_BACKEND = 'redis://'

The fields of the URL is defined as folows:

  • 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.

CELERY_REDIS_MAX_CONNECTIONS

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

MongoDB backend settings

Note

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

CELERY_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 pymongo docs to see a list of arguments supported.

Example configuration

CELERY_RESULT_BACKEND = 'mongodb://192.168.1.100:30000/'
CELERY_MONGODB_BACKEND_SETTINGS = {
    'database': 'mydb',
    'taskmeta_collection': 'my_taskmeta_collection',
}

Cassandra backend settings

Note

The Cassandra backend requires the pycassa library: http://pypi.python.org/pypi/pycassa/

To install the pycassa package use pip or easy_install:

$ pip install pycassa

This backend requires the following configuration directives to be set.

CASSANDRA_SERVERS

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

CASSANDRA_SERVERS = ['localhost:9160']

CASSANDRA_KEYSPACE

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

CASSANDRA_KEYSPACE = 'tasks_keyspace'

CASSANDRA_COLUMN_FAMILY

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

CASSANDRA_COLUMN_FAMILY = 'tasks'

CASSANDRA_READ_CONSISTENCY

The read consistency used. Values can be ONE, QUORUM or ALL.

CASSANDRA_WRITE_CONSISTENCY

The write consistency used. Values can be ONE, QUORUM or ALL.

CASSANDRA_DETAILED_MODE

Enable or disable detailed mode. Default is False. This mode allows to use the power of Cassandra wide columns to store all states for a task as a wide column, instead of only the last one.

To use this mode, you need to configure your ColumnFamily to use the TimeUUID type as a comparator:

create column family task_results with comparator = TimeUUIDType;

CASSANDRA_OPTIONS

Options to be passed to the pycassa connection pool (optional).

Example configuration

CASSANDRA_SERVERS = ['localhost:9160']
CASSANDRA_KEYSPACE = 'celery'
CASSANDRA_COLUMN_FAMILY = 'task_results'
CASSANDRA_READ_CONSISTENCY = 'ONE'
CASSANDRA_WRITE_CONSISTENCY = 'ONE'
CASSANDRA_DETAILED_MODE = True
CASSANDRA_OPTIONS = {
    'timeout': 300,
    'max_retries': 10
}

IronCache backend settings

Note

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

To install the iron_celery package use pip or easy_install:

$ pip install iron_celery

IronCache is configured via the URL provided in CELERY_RESULT_BACKEND, for example:

CELERY_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

Couchbase backend settings

Note

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

To install the couchbase package use pip or easy_install:

$ pip install couchbase

This backend can be configured via the CELERY_RESULT_BACKEND set to a couchbase URL:

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

CELERY_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).

AMQP backend settings

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:

CELERY_TASK_RESULT_EXPIRES = None

CELERY_RESULT_EXCHANGE

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

CELERY_RESULT_EXCHANGE_TYPE

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

CELERY_RESULT_PERSISTENT

If set to 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

CELERY_RESULT_BACKEND = 'amqp'
CELERY_TASK_RESULT_EXPIRES = 18000  # 5 hours.

Message Routing

CELERY_QUEUES

Most users will not want to specify this setting and should rather use the automatic routing facilities.

If you really want to configure advanced routing, this setting should be a list of 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 Basics for more information.

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

See also CELERY_ROUTES

CELERY_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 celery.routes.MapRoute instance.

Examples:

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

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

Where myapp.tasks.Router could be:

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 CELERY_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 apply_async() has these arguments:

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

and a router returns:

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

the final message options will be:

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

(and any default message options defined in the Task class)

Values defined in CELERY_ROUTES have precedence over values defined in CELERY_QUEUES when merging the two.

With the follow settings:

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

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

The final routing options for tasks.add will become:

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

See Routers for more examples.

CELERY_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):

CELERY_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:

CELERY_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.

CELERY_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:

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

CELERY_CREATE_MISSING_QUEUES

If enabled (default), any queues specified that are not defined in CELERY_QUEUES will be automatically created. See Automatic routing.

CELERY_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 CELERY_QUEUES. If CELERY_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.

See also

Changing the name of the default queue

CELERY_DEFAULT_EXCHANGE

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

The default is: celery.

CELERY_DEFAULT_EXCHANGE_TYPE

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

CELERY_DEFAULT_ROUTING_KEY

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

The default is: celery.

CELERY_DEFAULT_DELIVERY_MODE

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

Broker Settings

CELERY_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 Security for more.

Example:

# using serializer name
CELERY_ACCEPT_CONTENT = ['json']

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

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

BROKER_TRANSPORT

Aliases:BROKER_BACKEND
Deprecated aliases:
 CARROT_BACKEND

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 BROKER_FAILOVER_STRATEGY.

See URLs in the Kombu documentation for more information.

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 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).

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 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).

BROKER_USE_SSL

transports supported:
 pyamqp

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.

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:

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 will not validate the server cert at all. Please read Python ssl module security considerations.

BROKER_POOL_LIMIT

New in version 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 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.

BROKER_CONNECTION_TIMEOUT

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

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 BROKER_CONNECTION_MAX_RETRIES is exceeded.

This behavior is on by default.

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 0 or None, we will retry forever.

Default is 100 retries.

BROKER_LOGIN_METHOD

Set custom amqp login method, default is AMQPLAIN.

BROKER_TRANSPORT_OPTIONS

New in version 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):

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

Task execution settings

CELERY_ALWAYS_EAGER

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

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

CELERY_EAGER_PROPAGATES_EXCEPTIONS

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

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

CELERY_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 CELERY_STORE_ERRORS_EVEN_IF_IGNORED.

CELERY_MESSAGE_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.

CELERY_TASK_RESULT_EXPIRES

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

A built-in periodic task will delete the results after this time (celery.task.backend_cleanup).

A value of 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.

CELERY_MAX_CACHED_RESULTS

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 100. 0 or None means no limit, and a value of -1 will disable the cache.

CELERY_CHORD_PROPAGATES

New in version 3.0.14.

This setting defines what happens when a task part of a chord raises an exception:

  • If propagate is True the chord callback will change state to FAILURE with the exception value set to a ChordError instance containing information about the error and the task that failed.

    This is the default behavior in Celery 3.1+

  • If propagate is False the exception value will instead be forwarded to the chord callback.

    This was the default behavior before version 3.1.

CELERY_TRACK_STARTED

If True the task will report its status as “started” when the task is executed by a worker. The default value is 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.

CELERY_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 kombu.serialization.registry.

See also

Serializers.

CELERY_TASK_PUBLISH_RETRY

New in version 2.2.

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

Enabled by default.

CELERY_TASK_PUBLISH_RETRY_POLICY

New in version 2.2.

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

See Message Sending Retry for more information.

CELERY_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.

CELERY_DISABLE_RATE_LIMITS

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

CELERY_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.

See also

FAQ: Should I use retry or acks_late?.

Worker

CELERY_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.

CELERY_INCLUDE

Exact same semantics as CELERY_IMPORTS, but can be used as a means to have different import categories.

The modules in this setting are imported after the modules in CELERY_IMPORTS.

CELERYD_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 WorkerLostError exception.

Default is 10.0

CELERYD_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.

CELERYD_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.

CELERYD_TASK_SOFT_TIME_LIMIT

Task soft time limit in seconds.

The 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:

from celery.exceptions import SoftTimeLimitExceeded

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

CELERY_STORE_ERRORS_EVEN_IF_IGNORED

If set, the worker stores all task errors in the result store even if Task.ignore_result is on.

CELERYD_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 --statedb argument to worker.

Not enabled by default.

CELERYD_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.

CELERY_ENABLE_REMOTE_CONTROL

Specify if remote control of the workers is enabled.

Default is True.

Error E-Mails

CELERY_SEND_TASK_ERROR_EMAILS

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

Disabled by default.

ADMINS

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

SERVER_EMAIL

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

EMAIL_HOST

The mail server to use. Default is localhost.

EMAIL_HOST_USER

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

EMAIL_HOST_PASSWORD

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

EMAIL_PORT

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

EMAIL_USE_SSL

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

EMAIL_USE_TLS

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

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.

Example E-Mail configuration

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

# Enables error emails.
CELERY_SEND_TASK_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'

Events

CELERY_SEND_EVENTS

Send events so the worker can be monitored by tools like celerymon.

CELERY_SEND_TASK_SENT_EVENT

New in version 2.2.

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

Disabled by default.

CELERY_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.

CELERY_EVENT_QUEUE_EXPIRES

transports supported:
 amqp

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

Default is never, relying on the queue autodelete setting.

CELERY_EVENT_SERIALIZER

Message serialization format used when sending event messages. Default is json. See Serializers.

Broadcast Commands

CELERY_BROADCAST_QUEUE

Name prefix for the queue used when listening for broadcast messages. The workers host name will be appended to the prefix to create the final queue name.

Default is celeryctl.

CELERY_BROADCAST_EXCHANGE

Name of the exchange used for broadcast messages.

Default is celeryctl.

CELERY_BROADCAST_EXCHANGE_TYPE

Exchange type used for broadcast messages. Default is fanout.

Logging

CELERYD_HIJACK_ROOT_LOGGER

New in version 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 CELERYD_HIJACK_ROOT_LOGGER = False.

Note

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

CELERYD_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.

CELERYD_LOG_FORMAT

The format to use for log messages.

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

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

CELERYD_TASK_LOG_FORMAT

The format to use for log messages logged in tasks. Can be overridden using the --loglevel option to worker.

Default is:

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

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

CELERY_REDIRECT_STDOUTS

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

Enabled by default. Used by celery worker and celery beat.

CELERY_REDIRECT_STDOUTS_LEVEL

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

Default is WARNING.

Security

CELERY_SECURITY_KEY

New in version 2.5.

The relative or absolute path to a file containing the private key used to sign messages when Message Signing is used.

CELERY_SECURITY_CERTIFICATE

New in version 2.5.

The relative or absolute path to an X.509 certificate file used to sign messages when Message Signing is used.

CELERY_SECURITY_CERT_STORE

New in version 2.5.

The directory containing X.509 certificates used for Message Signing. Can be a glob with wildcards, (for example /etc/certs/*.pem).

Custom Component Classes (advanced)

CELERYD_POOL

Name of the pool class used by the worker.

Eventlet/Gevent

Never use this option to select the eventlet or gevent pool. You must use the -P option to celery worker instead, to ensure the monkey patches are not applied too late, causing things to break in strange ways.

Default is celery.concurrency.prefork:TaskPool.

CELERYD_POOL_RESTARTS

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

Disabled by default.

CELERYD_AUTOSCALER

New in version 2.2.

Name of the autoscaler class to use.

Default is celery.worker.autoscale:Autoscaler.

CELERYD_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.

CELERYD_CONSUMER

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

CELERYD_TIMER

Name of the ETA scheduler class used by the worker. Default is celery.utils.timer2.Timer, or one overrided by the pool implementation.

Periodic Task Server: celery beat

CELERYBEAT_SCHEDULE

The periodic task schedule used by beat. See Entries.

CELERYBEAT_SCHEDULER

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

Can also be set via the -S argument to beat.

CELERYBEAT_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 --schedule argument to beat.

CELERYBEAT_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.

CELERYBEAT_MAX_LOOP_INTERVAL

The maximum number of seconds 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 (-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.

Monitor Server: celerymon

CELERYMON_LOG_FORMAT

The format to use for log messages.

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

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