Top Celery Interview Questions and Answers (2024)

1. What is Celery?

2. What's a Task Queue in Celery?

3. What are the components of celery?

4. Can celery work without broker?

5. How to check task status in Celery?

6. How do I stop celery task?

7. What is the difference between celery and RabbitMQ?

Q: What is Celery?
Ans:

Celery is an open source asynchronous task queue or job queue that uses distributed message passing. Although it allows for scheduling, its primary emphasis is on real-time operations.

Q: What's a Task Queue in Celery?
Ans:

Task queues are used to distribute work among threads or machines. The input to a task queue is a unit of work known as a task. Job queues are continually monitored by dedicated worker processes for new work to do.

Q: What are the components of Celery?
Ans:

Celery's internal workings can be summarised as the Producer/Consumer model. Producers queue the jobs, and customers pull them from the queue. Celery has three key components.

1. Producers are usually the 'web nodes', or the web service processes that handle the web request. Tasks are assigned to Celery and placed into the task queue during request processing.
2. Queue is the broker that facilitates the transfer of tasks from a web application to a Celery worker (s). Celery has full support for RabbitMQ and Redis, as well as minimal support for Amazon SQS and Zookeeper (RabbitMQ docs).
3. Consumers are 'worker nodes' who listen to the queue head and consume and execute tasks as they are published. Workers may also publish back to the queue, triggering additional tasks, and thus acting as producers.

Q: Can celery work without broker?
Ans:

Celery communicates through messages, with a broker normally acting as a go-between for clients and workers. To begin a task, a client adds a message to the queue, which is then sent to a worker by the broker. As a broker, you can use the existing MongoDB database.

Q: How to check task status in Celery?
Ans:

Every Task object has a .request property that holds an AsyncRequest object. As a result, the following line describes the state of a Task task:

task.AsyncResult(task.request.id).state

Q: How do I stop celery task?
Ans:

The API for revoking tasks has been updated in Celery 3.1.
You should use result.revoke, as per Celery FAQ:

>>> result = add.apply_async(args=[2, 2], countdown=120)
>>> result.revoke()

Alternatively, if you just have the task id:

>>> from proj.celery import app
>>> app.control.revoke(task_id)

Q: What is the difference between celery and RabbitMQ?
Ans:

• Celery

  Task queue that is distributed. Celery is an asynchronous task/job queue that uses distributed message passing. It is designed for real-time operation, but it also supports scheduling.

• RabbitMQ

  A messaging broker is a messaging intermediary.