Periodic tasks with Celery Beat in Django - Mini Project: Build & Apply

Periodic tasks with Celery Beat

📖 Scenario: You are building a Django app that needs to perform a task regularly, like sending reminder emails every minute. To do this, you will use Celery with Celery Beat to schedule periodic tasks.

🎯 Goal: Create a Django project setup with Celery and Celery Beat. Define a simple periodic task that runs every minute and prints a message to the console.

📋 What You'll Learn

Create a Celery app instance in a file named celery.py inside your Django project directory.

Add a periodic task schedule in Celery Beat to run every minute.

Define a simple Celery task function called print_hello that prints 'Hello from Celery Beat!' to the console.

Configure Celery Beat in Django settings to enable periodic task scheduling.

💡 Why This Matters

🌍 Real World

Many web applications need to perform background jobs regularly, such as sending emails, cleaning up data, or updating caches. Celery Beat helps schedule these tasks easily.

💼 Career

Understanding how to set up periodic tasks with Celery Beat is valuable for backend developers working with Django to automate routine jobs efficiently.

1

Create Celery app instance

Create a file named celery.py in your Django project directory. Inside it, write code to create a Celery app instance called app with the project name 'myproject'. Import Django settings and configure Celery to use them.

Django

# Your code here to create Celery app instance

Hint

Use Celery('myproject') to create the app. Set the environment variable for Django settings before creating the app.

2

Add Celery Beat schedule configuration

In your Django settings file, add a dictionary called CELERY_BEAT_SCHEDULE. Inside it, add a task named 'print-hello-every-minute' that runs the task 'myapp.tasks.print_hello' every 60 seconds.

Django

from celery import Celery
import os

os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'myproject.settings')

app = Celery('myproject')
app.config_from_object('django.conf:settings', namespace='CELERY')
app.autodiscover_tasks()

# Add CELERY_BEAT_SCHEDULE dictionary in settings.py

Hint

Define CELERY_BEAT_SCHEDULE as a dictionary with the task name as key and a dictionary with task and schedule keys.

3

Define the periodic task function

In your Django app folder named myapp, create or edit the tasks.py file. Define a Celery task function called print_hello that prints the string 'Hello from Celery Beat!'. Use the @app.task decorator imported from the Celery app instance.

Django

from celery import Celery
import os

os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'myproject.settings')

app = Celery('myproject')
app.config_from_object('django.conf:settings', namespace='CELERY')
app.autodiscover_tasks()

# In myapp/tasks.py
# Your code here to define print_hello task

Hint

Import app from your Celery instance and decorate the function with @app.task.

4

Enable Celery Beat in Django settings

In your Django settings file, add django_celery_beat to the INSTALLED_APPS list to enable Celery Beat integration.

Django

from celery import Celery
import os

os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'myproject.settings')

app = Celery('myproject')
app.config_from_object('django.conf:settings', namespace='CELERY')
app.autodiscover_tasks()

# In settings.py
CELERY_BEAT_SCHEDULE = {
    'print-hello-every-minute': {
        'task': 'myapp.tasks.print_hello',
        'schedule': 60.0
    },
}

# Add django_celery_beat to INSTALLED_APPS below

Hint

Add 'django_celery_beat' exactly to the INSTALLED_APPS list in settings.py.

Practice

1. What is the main purpose of Celery Beat in a Django project?

easy

A. To schedule and run periodic tasks automatically

B. To handle HTTP requests asynchronously

C. To manage database migrations

D. To serve static files efficiently

Solution

1. Step 1: Understand Celery Beat's role

   Celery Beat is designed to schedule tasks to run at specific times or intervals automatically.

2. Step 2: Differentiate from other components

   Handling HTTP requests, managing migrations, or serving static files are not functions of Celery Beat.

3. Final Answer:

   To schedule and run periodic tasks automatically -> Option A

4. Quick Check:

   Celery Beat = periodic task scheduler [OK]

Hint: Celery Beat schedules tasks, not handles requests [OK]

Common Mistakes:

• Confusing Celery Beat with Django's request handling
• Thinking Celery Beat manages database or static files
• Assuming Celery Beat runs tasks immediately without schedule

2. Which of the following is the correct way to define a periodic task schedule using Celery Beat with a crontab in Django settings?

easy

A. "beat_schedule = { 'task-name': { 'task': 'app.tasks.my_task', 'schedule': crontab(minute='0', hour='*/3') } }"

B. "beat_schedule = { 'task-name': { 'task': 'app.tasks.my_task', 'schedule': crontab('0', '*/3') } }"

C. "beat_schedule = { 'task-name': { 'task': 'app.tasks.my_task', 'schedule': crontab(minute=0, hour='every 3 hours') } }"

D. "beat_schedule = { 'task-name': { 'task': 'app.tasks.my_task', 'schedule': crontab(minute='0', hour='3/0') } }"

Solution

1. Step 1: Check crontab syntax

   The crontab function requires named arguments like minute and hour with string values representing schedule patterns.

2. Step 2: Validate correct usage

   "beat_schedule = { 'task-name': { 'task': 'app.tasks.my_task', 'schedule': crontab(minute='0', hour='*/3') } }" correctly uses crontab(minute='0', hour='*/3') to run every 3 hours at minute 0.

3. Final Answer:

   beat_schedule with crontab(minute='0', hour='*/3') -> Option A

4. Quick Check:

   Correct crontab syntax = "beat_schedule = { 'task-name': { 'task': 'app.tasks.my_task', 'schedule': crontab(minute='0', hour='*/3') } }" [OK]

Hint: Use named args with strings in crontab() [OK]

Common Mistakes:

• Passing positional arguments instead of named
• Using invalid hour format like '3/0'
• Mixing string and integer types incorrectly

3. Given this Celery Beat schedule snippet in Django settings:

beat_schedule = {
  'print-time': {
    'task': 'app.tasks.print_time',
    'schedule': crontab(minute='*/15')
  }
}

What will happen when Celery Beat and worker run?

medium

A. The task will not run due to syntax error

B. The task runs only once at minute 15

C. The task runs every hour at minute 0

D. The task 'print_time' runs every 15 minutes

Solution

1. Step 1: Interpret crontab(minute='*/15')

   This means the task runs every 15 minutes, at minute 0, 15, 30, 45 of each hour.

2. Step 2: Understand Celery Beat behavior

   When both Beat and worker run, Beat triggers the task on schedule, so it runs repeatedly every 15 minutes.

3. Final Answer:

   The task 'print_time' runs every 15 minutes -> Option D

4. Quick Check:

   crontab '*/15' means every 15 minutes [OK]

Hint: */15 in crontab means every 15 minutes [OK]

Common Mistakes:

• Thinking it runs only once
• Confusing minute '*/15' with fixed minute 15
• Assuming syntax error without checking carefully

4. You defined this schedule in your Django settings:

beat_schedule = {
  'cleanup-task': {
    'task': 'app.tasks.cleanup',
    'schedule': crontab(minute=0, hour='*')
  }
}

But the task never runs. What is the most likely cause?

medium

A. The task name 'cleanup-task' is invalid

B. You forgot to start the Celery Beat service

C. The crontab syntax is incorrect because minute should be a string

D. The worker must be restarted every hour

Solution

1. Step 1: Check if Celery Beat is running

   Celery Beat must be running to send scheduled tasks to the worker.

2. Step 2: Validate other options

   Task names can be any string, crontab accepts integer or string for minute, and workers do not need hourly restart.

3. Final Answer:

   You forgot to start the Celery Beat service -> Option B

4. Quick Check:

   Beat service must run for schedules to trigger [OK]

Hint: Always run Celery Beat alongside worker [OK]

Common Mistakes:

• Assuming task name format causes failure
• Thinking crontab minute must be string only
• Restarting worker unnecessarily

5. You want to run a Django Celery task every day at 2:30 AM and also every 10 minutes. How should you configure beat_schedule to achieve this?

hard

A. { 'daily-task': { 'task': 'app.tasks.daily', 'schedule': crontab(hour='2:30') }, 'frequent-task': { 'task': 'app.tasks.frequent', 'schedule': crontab(minute=10) } }

B. { 'daily-task': { 'task': 'app.tasks.daily', 'schedule': crontab(hour=2, minute=30) }, 'frequent-task': { 'task': 'app.tasks.frequent', 'schedule': crontab(minute=10) } }

C. { 'daily-task': { 'task': 'app.tasks.daily', 'schedule': crontab(hour=2, minute=30) }, 'frequent-task': { 'task': 'app.tasks.frequent', 'schedule': crontab(minute='*/10') } }

D. { 'daily-task': { 'task': 'app.tasks.daily', 'schedule': crontab(hour='2', minute='30') }, 'frequent-task': { 'task': 'app.tasks.frequent', 'schedule': crontab(minute='10') } }

Solution

1. Step 1: Define daily task schedule correctly

   Use crontab(hour=2, minute=30) or with strings '2' and '30' to run at 2:30 AM daily.

2. Step 2: Define frequent task schedule correctly

   Use crontab(minute='*/10') to run every 10 minutes; minute=10 runs only at minute 10 each hour.

3. Step 3: Check all options

   { 'daily-task': { 'task': 'app.tasks.daily', 'schedule': crontab(hour=2, minute=30) }, 'frequent-task': { 'task': 'app.tasks.frequent', 'schedule': crontab(minute='*/10') } } uses correct crontab syntax for both tasks; others have invalid formats or misunderstandings.

4. Final Answer:

   Use crontab(hour=2, minute=30) and crontab(minute='*/10') -> Option C

5. Quick Check:

   Daily at 2:30 and every 10 min = { 'daily-task': { 'task': 'app.tasks.daily', 'schedule': crontab(hour=2, minute=30) }, 'frequent-task': { 'task': 'app.tasks.frequent', 'schedule': crontab(minute='*/10') } } [OK]

Hint: Use '*/10' for every 10 minutes, not minute=10 [OK]

Common Mistakes:

• Using '2:30' as hour value
• Setting minute=10 instead of '*/10' for intervals
• Mixing string and integer types incorrectly