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Scheduled tasks

Prerequisites:

  • Your solution is based on lime-crm 2.80.0 or later

Scheduling tasks

Scheduling tasks in Lime CRM is easy. The only thing you have to do is to write a few lines of code in your solution/limepkg.

Run the following command to scaffold a scheduled task for your solution:

lime-project generate scheduled-tasks

The command above adds the function register_scheduled_tasks to the solution's tasks package. Your tasks/__init__.py module will look similar to the example below:

from . import tasks
from lime_task.schedule import (
    CronTab,
    ScheduledTask,
    TaskSession)


def get_task_modules():
    """List all task modules that lime-task-handler should register"""
    return [tasks]


def register_scheduled_tasks():
    return[
        ScheduledTask(
            task=tasks.my_task,
            session=TaskSession(
                user_name='integration-user',
                language='sv'),
            args=['arg1', {'test': 'test'}, True, 1337, None],
            schedule=CronTab(hour=7, minute=30, day_of_week=1))
    ]

The code above defines the function register_scheduled_tasks and returns a list of ScheduledTask instances. Tasks returned by this function will be scheduled in Lime CRM.

For each ScheduledTask instance you have to configure the following:

  • Which task to run. This is the actual task function (decorated with @task) that you want to execute.
  • A SessionTask, i.e. which user should run the task and under what language.
  • A schedule, i.e. describe when the task should run and how often.
  • Arguments that should be sent to the task. The first argument to a task will always be the LimeApplication instance. But if you have a task that takes additional arguments it's possible to send them in via the args argument.

Check content of init.py file

If you create the scheduled-task in an old solution, you need to check that you have this in the init.py file in the root of the solution: 

try:
    from .tasks import register_scheduled_tasks  # noqa
except ImportError:
    logger.info('solution_xxxxxxxx doesn\'t implement any scheduled tasks')
Otherwise, the scheduled-tasks won't be registered as scheduling tasks. New solutions should already have this generated from the lime-project new solution templates.

Configure the schedule

You configure the schedule for a task by creating a CronTab instance. The CronTab instance is defined in lime_task but is actually just a wrapper around the Celery Crontab scheduler. Please checkout the celery documentation for information about how to use it.

Warning

Ensure that the taskhandler (and the scheduler) is up and running. Otherwise your scheduled tasks will not be run.

Disable a scheduled task

It's possible to temporarily disable a task.

Note

A disabled task remains scheduled but will not be executed. A "dummy" function with information logs about the disabled task will be run instead.

You disable a task via the Application Configuration. (Read more here)

In the following example, the task my_solution.tasks.my_tasks.my_special_task has been disabled:

config:
  tasks:
    scheduled_tasks:
      my_solution.tasks.my_tasks.my_special_task:
        enabled: False

Tip

remember to use the full path to your task, otherwise it will not be disabled

Error handling

It's important to know if a scheduled task failed. It's therefore possible to create an event handler that reacts to either succeeding or failing tasks. Read more about event handlers here and more about task events here

Services

You can find more information on the task-handler service here.

Windows

Scheduled tasks are dispatched by the lime-task-scheduler and run by the lime-task-handler. That means that you have to ensure that both services are running. If it's only the scheduler that's running, a scheduled task will be dispatched, but never run.

Linux/Mac OS

Scheduled tasks are run and dispatched by the same service.