Periodic tasks with Celery Beat in Django - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when a periodic task is scheduled with Celery Beat?

Consider a Django project using Celery and Celery Beat. If you schedule a periodic task to run every 10 minutes, what will Celery Beat do?

A Celery Beat only logs the task schedule but does not trigger any execution.

B Celery Beat sends a message to the Celery worker every 10 minutes to execute the task.

C Celery Beat stores the task results every 10 minutes but does not trigger execution.

D Celery Beat runs the task itself every 10 minutes without involving Celery workers.

💡 Hint

Think about how Celery Beat interacts with Celery workers to run tasks.

Celery Beat acts as a scheduler. It sends messages to Celery workers at the scheduled times to run the tasks. It does not run tasks itself.

📝 Syntax

intermediate

Which Celery Beat schedule syntax correctly runs a task every hour?

Given the following Celery Beat schedule snippet, which option correctly schedules a task to run every hour?

Django

from celery.schedules import crontab

CELERY_BEAT_SCHEDULE = {
    'task-every-hour': {
        'task': 'myapp.tasks.my_task',
        'schedule': ???
    }
}

A crontab(minute=0, hour='*')

B crontab(minute='*', hour=0)

C crontab(minute=0, hour=0)

D crontab(minute='0', hour='0-59')

💡 Hint

An hourly task runs at minute 0 of every hour.

Using crontab(minute=0, hour='*') schedules the task to run at the start of every hour.

🔧 Debug

advanced

Why does a periodic task not run even though Celery Beat is running?

You have Celery Beat running and a periodic task scheduled. However, the task never executes. Which of the following is the most likely cause?

A The periodic task schedule is set to a past date.

B Celery Beat is running with the wrong timezone setting.

C The task function is missing a @shared_task decorator.

D Celery worker is not running or not connected to the message broker.

💡 Hint

Celery Beat only sends messages; workers must be ready to receive them.

If the Celery worker is not running or cannot connect to the broker, tasks will not execute even if Celery Beat schedules them.

❓ state_output

advanced

What is the state of a periodic task after Celery Beat triggers it?

When Celery Beat triggers a periodic task, what is the expected state of the task in Celery's task monitoring system immediately after triggering?

A The task state is 'PENDING' until a worker picks it up.

B The task state is 'STARTED' immediately after Celery Beat triggers it.

C The task state is 'RETRY' until the task completes.

D The task state is 'SUCCESS' immediately after Celery Beat triggers it.

💡 Hint

Think about when the task actually starts running.

After Celery Beat sends the task message, the task is 'PENDING' until a worker receives and starts it.

🧠 Conceptual

expert

How does Celery Beat ensure periodic tasks run on schedule in a distributed system?

In a distributed Django application with multiple Celery Beat instances running for redundancy, how does Celery Beat prevent the same periodic task from running multiple times simultaneously?

A Celery Beat instances communicate over the network to elect a leader manually.

B Each Celery Beat instance runs the task independently, and Celery workers deduplicate tasks.

C Celery Beat uses a distributed lock in the message broker or database to allow only one scheduler to send task messages.

D Celery Beat disables periodic tasks on all but one instance automatically.

💡 Hint

Think about how distributed systems avoid duplicate work.

Celery Beat uses distributed locking mechanisms (like locks in Redis or the database) to ensure only one scheduler instance sends task messages at a time.