Django Celery Logging Best Practice

Question

I'm trying to get Celery logging working with Django. I have logging set-up in settings.py to go to console (that works fine as I'm hosting on Heroku). At the top of each module, I have:

import logging
logger = logging.getLogger(__name__)

And in my tasks.py, I have:

from celery.utils.log import get_task_logger
logger = get_task_logger(__name__)

That works fine for logging calls from a task and I get output like this:

2012-11-13T18:05:38+00:00 app[worker.1]: [2012-11-13 18:05:38,527: INFO/PoolWorker-2] Syc feed is starting

But if that task then calls a method in another module, e.g. a queryset method, I get duplicate log entries, e.g.

2012-11-13T18:00:51+00:00 app[worker.1]: [INFO] utils.generic_importers.ftp_processor process(): File xxx.csv already imported. Not downloaded
2012-11-13T18:00:51+00:00 app[worker.1]: [2012-11-13 18:00:51,736: INFO/PoolWorker-6] File xxx.csv already imported. Not downloaded

I think I could use

CELERY_HIJACK_ROOT_LOGGER = False

to just use the Django logging but this didn't work when I tried it and even if I did get it to work, I would lose the "PoolWorker-6" bit which I do want. (Incidentally, I can't figure out how to get the task name to display in the log entry from Celery, as the docs seems to indicate that it should).

I suspect I'm missing something simple here.

Answer 1

When your logger initialized in the beginning of "another module" it links to another logger. Which handle your messages. It can be root logger, or usually I see in Django projects - logger with name ''.

Best way here, is overriding your logging config:

LOGGING = {
    'version': 1,
    'disable_existing_loggers': True,
    'formatters': {
        'simple': {
            'format': '%(levelname)s %(message)s',
             'datefmt': '%y %b %d, %H:%M:%S',
            },
        },
    'handlers': {
        'console': {
            'level': 'DEBUG',
            'class': 'logging.StreamHandler',
            'formatter': 'simple'
        },
        'celery': {
            'level': 'DEBUG',
            'class': 'logging.handlers.RotatingFileHandler',
            'filename': 'celery.log',
            'formatter': 'simple',
            'maxBytes': 1024 * 1024 * 100,  # 100 mb
        },
    },
    'loggers': {
        'celery': {
            'handlers': ['celery', 'console'],
            'level': 'DEBUG',
        },
    }
}

from logging.config import dictConfig
dictConfig(LOGGING)

In this case I suppose it should work as you assume.

P.S. dictConfig added in Python2.7+.

Answer 2

It is troubling that Celery interferes with the root logger (which is not best practice and can't be controlled completely), but it does not disable your app's custom loggers in any way, so use your own handler names and define your own behavior rather than trying to fix this issue with Celery. [I like to keep my application logging separate anyway). You could use separate handlers or the same for Django code and Celery tasks, you just need to define them in your Django LOGGING config. Add formatting args for module, filename, and processName to your formatter for sanity, to help you distinguish where messages originate.

[this assumes you have setup a handler for 'yourapp' in the LOGGING settings value that points to an Appender - sounds like you are aware of this though].

views.py

log = logging.getLogger('yourapp')
def view_fun():
    log.info('about to call a task')
    yourtask.delay()

tasks.py

log = logging.getLogger('yourapp')
@task
def yourtask():
    log.info('doing task')

For the logging that Celery generates - use the celeryd flags --logfile to send Celery output (eg, worker init, started task, task failed) to a separate place if desired. Or, use the other answer here that sends the 'celery' logger to a file of your choosing.

Note: I would not use RotatingFileHandlers - they are not supported for multi-process apps. Log rotation from another tool like logrotate is safer, same goes with logging from Django assuming you have multiple processes there, or the same log files are shared with the celery workers. If your using a multi-server solution you probably want to be logging somewhere centralized anyway.

Answer 3

To fix duplicate logging issue, what worked for me is to set the propagate setting to false when declaring my settings.LOGGING dict

LOGGING = {
    'version': 1,
    'disable_existing_loggers': False,
    'handlers': {
        'console': {
            'level': 'DEBUG',
            'class': 'logging.StreamHandler',
            'formatter': 'verbose'
        },
    },
    'formatters': {
        'verbose': {
            'format': '%(asctime)s %(levelname)s module=%(module)s, '
            'process_id=%(process)d, %(message)s'
        }
    },
    'loggers': {
        'my_app1': {
            'handlers': ['console'],
            'level': 'DEBUG',
            'propagate': False #this will do the trick
        },
        'celery': {
            'handlers': ['console'],
            'level': 'DEBUG',
            'propagate': True
        },
    }
}

lets say your django project layout looks like:
my_project/
- tasks.py
- email.py

and lets say one of your tasks makes a call to some function in email.py; the logging will happen in email.py and then that logging will get propagated to the 'parent' which in this case happens to be your celery task. Thus double logging. But setting propagate to False for a particular logger means that for that logger/app, its logs wont get propagated to the parent, hence their will be no 'double' logging. By default 'propagate' is set to True

Here's a link to the django docs section about that parent/children loggers stuff