This talk is from Open Source Summit 2022 Apache Airflow 2.2 introduced the concept of Deferrable Tasks that uses Python's async feature. All the Airflow sensors and poll-based operators can be hugely optimized to save tons of money by freeing up worker slots when polling. This session will cover the following topics: - Introduction to the concept of deferrable operator - Why do we need them? - When to use them? - How does it work? - Writing Custom deferrable operators & Sensors

1. Airflow: Deferrable
“Async” Operators
How you can save tons of money!!
Kaxil Naik
Open Source Summit 2022

2. Who am I?
● Committer & PMC Member of Apache Airflow
● Director of Airflow Engineering @ Astronomer
@kaxil

3. What is Apache Airflow?

4. A platform to programmatically author,
schedule, and monitor workflows

5. Example DAG

6. Why deferrable operators?
The problem around current operators & sensors
What are they?
And how do they work?
Available async operators
How to find & use the available async operators

7. Why deferrable operators?

8. Scheduler
Time
Scheduler
Worker

9. Scheduler
Time
Scheduler
Submit Spark Job
Typical Operator
Poll Spark cluster Job Completion
Worker

10. Scheduler
Time
Scheduler
Typical Sensor
Wait for files to arrive in S3 Arrived!
Worker

11. Scheduler
Time
Scheduler
What a waste!
Wait for files to arrive in S3 Arrived!
Worker
Submit Spark Job Poll Spark cluster Job Completion
Wasted resources
Wasted resources
Operator
Sensor

12. Time
Polling for Spark Job completion Done!
Multiple
Sensors
Wait for files to arrive in S3 Done!
Polling for Bigquery Job completion Done!
Polling for Spark Job completion Done!
Wait for files to arrive in S3 Done!
Wait for files to arrive in GCS Done!
Imagine the Cost!
Multiple worker slots
Blocked !!

13. What are deferrable operators?

14. Scheduler
Time
Scheduler
Worker
Triggerer
Worker

15. Scheduler
Time
Scheduler
Submit Spark Job
Async Operator
Free slot Job Completion
Worker
Poll Spark cluster
Triggerer

16. Scheduler
Time
Scheduler
Task 1
Worker Slot (Sync vs Async)
Task 2
Sync
Operator
Async
Operator
Task 1 Task 2 Task 3 Task 2
Task 1 Task 4

17. Task runs on the Worker, then “defers” itself
Example: Submit an API call and stores job_id in DB
Runs on Triggerer
Async polling until the criteria is met, stores response in DB
Back to the Worker
To show response in the logs and set Task state

18. Scheduler
Time
Scheduler
Submit Spark Job
Async Operator
Free slot Job Completion
Worker
Poll Spark cluster
Triggerer
Trigger - a
new concept

19. Trigger is different than Operator

20. Must be asynchronous & quick
So Triggerer can run thousands of them per CPU core
Should not persistent state
So we can shuffle them around between Triggerers as needed
Must support running multiple copies of itself
For reliability during network partitions

21. class DateTimeTrigger(BaseTrigger):
def __init__(self, moment: datetime.datetime):
super().__init__()
self.moment = moment
def serialize(self):
return ("mymodule.DateTimeTrigger", {"moment": self.moment})
async def run(self):
while self.moment > timezone.utcnow():
await asyncio.sleep(1)
yield TriggerEvent(self.moment)

22. class WaitOneHourSensor(BaseSensorOperator):
def execute(self, context):
self.defer(
trigger=TimeDeltaTrigger(timedelta(hours=1)),
method_name="execute_complete",
)
def execute_complete(self, context, event=None):
# We have no more work to do here. Mark as complete.
return

23. Available Deferrable Operators

24. Core Airflow & Providers
https://github.com/apache/airflow/
Astronomer Providers
https://github.com/astronomer/astronomer-providers
50+ async operators

25. Astronomer Providers
https://github.com/astronomer/astronomer-providers
50+ async operators
Built and maintained with ❤ by Astronomer
Apache 2 licensed & Open-source
Drop-in replacements of “sync” Operators
Openlineage support

26. Astronomer Providers
https://github.com/astronomer/astronomer-providers
Async Operators available for:
● AWS, Google Cloud, Microsoft Azure
● Databricks, Snowflake
● Kubernetes, Apache Livy, Apache Hive
● HTTP, Filesystem

27. from astronomer.providers.amazon.aws.sensors.s3 import S3KeySensorAsync as S3KeySensor
waiting_for_s3_key = S3KeySensor(
task_id="waiting_for_s3_key"
,
bucket_key="sample_key.txt"
,
wildcard_match
=False,
bucket_name="sample-bucket"
,
)

28. Caveats when building one

29. More cost benefits when polling takes longer time
We've seen over a 90% reduction in resources for a 10 min wait
Not everything can be deferred
It must be an external event/system with a unique identifier
Triggerer logs are not visible in the Webserver/UI
Only task logs from workers are displayed on UI

30. Thank You
@kaxil