Most frequently asked Celery Interview Questions

1. What is Celery?
2. What are the components of celery?
3. What's the difference between Celeryd and Celerybeat?
4. Can we replace Celerybeat with Chronos?
5. What is a Broker?
6. How to check task status in Celery?
7. Why should we use Celery instead of RQ?
8. What is Celery worker?
9. In which language Celery is written?
10. What is the alternative to Celery Python?
11. How do I stop celery task?

What is Celery?

Celery is source which helps in distributing messages based on task queueor job queue.Celery is used by instagram, Mozilla Addons, etc, its focus is for operating in real time.
Features of Celery are:
Resource Leak Protection
High availability and horizontal scaling
Autoreloading and Resource Leak Protection
Workflows
Autoscaling
User Components

What are the components of celery?

• Producers handles web requests
• Queue helps passing tasks from web application
• Consumers helps to consume and execute whenever a taks is established

What's the difference between Celeryd and Celerybeat?

Celery executes tasks and Celerybeat schedules tasks.
Celery on a regular schedule helps to run batch jobs in the background while Celerybeat on the other hand is instructed on how to run all the tasks on a specific date or time.

Can we replace Celerybeat with Chronos?

Sure, we can replace celerybeat with chronos.Chronos supports RESTful submission of events with ISO8601 format and is useful for management as it can mitigate the necessity to use schedule tasks.

What is a Broker?

A broker is a connector between the workers and the clients.Here the broker can be Redis, Rabbitmq, etc that is coneying the message between workers and clients.
Below is a diagram that shows the connection of broker(rabbitmq) with the workers and clients.

How to check task status in Celery?

In order for Celery to record that a task is running, you must use:

example_task.status() == RUNNING

Why should we use Celery instead of RQ?

RQ uses only one broker(Redis) cannot switch brokers in the future if Redis no longer works, where as Celery has considered using both RabbitMQ and Redis.
RQ only supports one language that is Python and Celery can send the tasks from one language to different language.
Celery suppots Subtask whereas RQ does not suports.
Celery and RQ both are simple to setup and will give us all the information we need.

What is Celery worker?

Celery worker does not processes any tasks by itself other than Clery spawns child processes and deals all the book keeping.

In which language Celery is written?

It is written in Python Language.

What is the alternative to Celery Python?

Dramatiq is a fast and reliable alternative to Celery. It supports RabbitMQ and Redis as message brokers.

How do I stop celery task?

You should use result.revoke:

>>> result = add.apply_async(args=[2, 2], countdown=180)
>>> result.revoke()