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April 10th 2019
Tao Feng | @feng-tao | Software Engineer, Lyft
Airflow @ Lyft

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Who
● Tao Feng
● Engineer at Lyft Data Platform
● Apache Airflow PMC and Committer
● Working on different data products (Airflow,
Amundsen, etc)

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Agenda
• Airflow in general
• Airflow @ Lyft
• Upstream @ Lyft
• Next Step
• Summary
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Airflow in general
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Airflow in general
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• Airflow just became an Apache top level project(TLP) recently.
‒ Total 20 PMCs / committers
• Most recent release 1.10, 1.10.1, 1.10.2 (1.10.3 is coming).
‒ New Features: Airflow RBAC, Airflow K8S integration, etc
• New Process in Airflow for proposing architecture change.
‒ Airflow Improvements Proposals (currently 19+ proposals)
• Recent community conducted Airflow user survey (link).
11k+
github
stars
740+
contributors
250+
Companies
using

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Airflow @ Lyft
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Core Infra high level architecture @ Lyft

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Airflow Architecture @ Lyft
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Airflow Architecture @ Lyft
• WebUI: the portal for users to view the related status of the DAGs.
• Metadata DB: the Airflow metastore for storing various job status.
• Scheduler: a multi-process which parses the DAG bag, creates a DAG object and
triggers executor to execute those dependency met tasks.
• Executor: A message queuing process that orchestrates worker processes to execute
tasks. We uses CeleryExecutor at Lyft.
• TARS: Airflow development / backfill environment, which provides access to production
data. 9

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Airflow Architecture @ Lyft
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• Main Cluster Config: Apache Airflow 1.8.2 with cherry-picks and numerous in-
house Lyft patches.
• Scale: Three set of ASGs for workers.
‒ ASG #1: 15 worker nodes each of which is the r5.4xlarge (16vcpu, 128g mem) type. This fleet of
workers is for processing low-priority memory intensive tasks.
‒ ASG #2: 3 worker nodes each of which is the m4.4xlarge (16vcpu, 64g mem) )type. This fleet of
workers is dedicated for those DAGs with a strict SLA.
‒ ASG #3: 1 worker node with m4.10xlarge (40vcpu, 160g mem) type. The single node is used to
process the compute-intensive workloads from a critical team’s DAGs.
‒ Backfill Box(TARS): 1 node with m4.16xlarge (64vcpu, 256g mem) )type. This box is used for fast
DAG prototyping and backfill.

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Airflow daily stats @ Lyft
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600+
DAGs
800+
DagRuns
25k+
TIs

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Airflow Monitoring @
Lyft
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Airflow Availability
• Scheduler and worker health check
‒ Use Canary monitoring DAG.
‒ No task has been scheduled for 10 mins is considered downtime.
• UI health check
‒ Leverage Envoy membership health check.
• Total system Uptime pct
‒ Airflow is down if either scheduler, workers, or web server is down.
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Schedule Delay
• scheduler delay = TI.start_time - TI.execution_date
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DAG last run time
• The time that have elapsed since the DAG file was last processed.
• If the time becomes too long, it means scheduler has issues processing the
DAG files.
‒ E.g could due to parser threads occupied by malicious DAG files.
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Executor parallelism
• Parallelism: control the #. concurrent running tasks.
‒ Please monitor your worker nodes’ cpu utilization before increasing the value.
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Airflow monitoring @ Lyft
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Stats Name Meaning
dag_processing.last_run.seconds_ago.<d
ag_file>
Seconds since <dag_file> was last
processed
executor.open_slots Number of of open slots on executor
(parallelism - # running task)
executor.queued_tasks Number of queued tasks on executor
executor.running_tasks Number of running tasks on executor
pool.starving_tasks.<pool_name> Number of starving tasks in the pool.
Check how many tasks are starving due to
pool count limitation.
…...

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Airflow Customization
@ Lyft
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Airflow customization @ Lyft
• UI auditing
• Extra link for task instance UI panel (AIRFLOW-161)
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Airflow customization @ Lyft
• DAG dependency graph
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Improve Airflow
Reliability @ Lyft
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Improving Airflow Performance @ Lyft
• Reduce Airflow UI page load time
‒ Change default_dag_run_display_number to 5.
• Tunables that impacts tasks execution parallelisms
‒ Parallelism
‒ Concurrency
‒ Max_active_runs
‒ Pool
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Improving Airflow Reliability at Lyft
• Source Control For Pools
‒ All Airflow pools are defined in a source controlled github source file.
‒ Airflow pools are configured based on the file in runtime.
• Integration tests for DAG to enforce best practice and improve reliability
‒ All the DAGs should be loadable within time threshold.
‒ All the DAGs should have valid pools associated.
‒ External task sensors should be valid((dag_id, task_id) exists).
‒ Each pool is used by at least by one DAG.
‒ The sensor has a reasonable timeout.
‒ Each DAG has a non dynamic start date.
• Secure UI access
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Production Debug @
Lyft
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Production Debug @ Lyft
• We document every production issue investigation in the doc.
• Couples of methodologies:
‒ View the centralized Airflow dashboard.
‒ Identify whether it is UI or Airflow scheduler(backend) issues.
‒ View the webserver log or scheduler log.
∙ If the log is not available in machine, check the log in kibana.
∙ To further identify issues, we sometimes even look at logs in S3
‒ Use different tools for further investigation
∙ If exceptions is thrown, understand which part of Airflow code throws the exception.
∙ If CPU / memory alarm, use top to identify which DAG causes the issue.
∙ If failure related to celery, login to celery flower UI to further investigate.
∙ ...
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Airflow Gotchas @ Lyft
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Airflow Gotchas at Lyft
• DST
‒ UI doesn’t have timezone support even in upstream.
‒ Scheduler internal version has no timezone support.
• DAGs with dynamic start date.
‒ Hard to predict when the DAG is scheduled
• Long running external task sensors that don’t have valid external tasks.
• HivePartitionSensor doesn’t work for partial partition
‒ It only checks whether data exists, not check whether data fully loaded.
• Backfill experience
‒ We use local executor to backfill.
• Long running sensor occupies task slot of the pool
• User confused with DAG level argument vs Task level argument
‒ E.g Put max_active_run in default task argument
• Legacy high abstraction framework over Airflow
‒ Hard to debug for the user and us. 27

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Upstream @ Lyft
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Improve backfill
experience
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Improve backfill experience
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• New options for backfill
‒ --reset_dagruns: if used, Airflow will first check if there are any existing dag_runs /
task_instances associated with the backfill date range. If yes, it will prompt user whether the
user wants to clear those task_instances first. (AIRFLOW-2718)
‒ --rerun_failed_tasks: if used, Airflow automatically try to rerun those failed tasks again
without requiring any user intervention. (AIRFLOW-2566)
• Backfill respects pool for isolation (AIRFLOW-1557)

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Improve backfill experience
Support batch backfill
• Use {{ prev_ds }} and {{ ds }} in SQL
‒ Prev_ds equals to ds -
schedule_interval
‒ User could change the
schedule_interval in the DAG file
during backfill.
• Use could override dag param with -c
options during backfill.
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INSERT OVERWRITE TABLE {{
dest_db(default.superhero_data) }}
SELECT supe.superhero_name AS superhero_name,
pop.popularity AS popularity
FROM
{{ source_table(events.superheroes) }} supe
WHERE {{ prev_ds }} >= ds AND ds < {{ ds }}
airflow backfill superheroes -s 2018-05-01 -e
2018-05-08 -c {‘hive_cluster’:
‘backfill_cluster’}

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Airflow DAG level
access
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Airflow DAG level access @ Lyft
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• DAG access control has always been a real need at Lyft
‒ HR data, Financial data, etc
‒ The workaround is to build an isolated dedicated cluster for each use case.
• Airflow introduces the RBAC feature in 1.10
‒ Airflow new webserver is based on Flask-Appbuilder.
‒ Ships with 5 static roles(Admin, User, Op, Viewer, Public).
‒ ...
• Airflow DAG level access (AIRFLOW-2267)
‒ Provides additional granular access control on DAG level.

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Airflow DAG level access @ Lyft
• New Airflow UI migrates from Flask-Admin to Flask-Appbuilder(FAB).
• FAB’s security model.
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Airflow DAG level access @ Lyft
• Which Airflow includes the change?
‒ 1.10.2 includes initial implementation
‒ 1.10.3(upcoming) includes the enhancements
• How it works
‒ Two new perms: can_dag_read (read), can_dag_edit (write).
‒ DAG level role could be created through cli / UI by Admin (doc).
‒ DAG level role could only see the viewable DAGs.
‒ User could declare permissions in DAG file (AIRFLOW-2694).
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Airflow DAG level access @ Lyft
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• We build a new cluster based on
Airflow master branch and
onboard couples of new sensitive
data use cases.
‒ Each use case has its own repo.
‒ User role relationship source
controlled in a YAML file.
• DAG owners specify the access
control info in the DAG files.
• Gotchas
‒ New user onboarding
‒ Integration between FAB and
google authentication(OAUTH)
‒ Integration with internal ACL
service
‒ ...
User registration flow

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Next Step
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Next Step
• Support Airflow DAG level access feature in beta internally.
• Integrate Airflow RBAC / DAG level feature with internal ACL service(FAB issue).
• Migrate all the existing DAGs to this new cluster.
• Explore running Airflow with k8s executor internally.
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Summary
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Summary
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• Airflow community has been growing a lot!
• We share our experience on operating Airflow at Lyft.
• We share some of our upstream work
‒ Improve Airflow backfill experience
‒ Support Airflow DAG level Access

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Acknowledgement
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• Members who maintain Airflow at Lyft
‒ Alagappan Sethuraman
‒ Andrew Stahlman
‒ Chao-han Tsai
‒ Jinhyuk Chang
‒ Junda Yang
‒ Max Payton
‒ Tao Feng
• Special thanks to Maxime Beauchemin who provides numerous suggestions for
us.

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Tao Feng | @feng-tao
Slides at TBD
Blog at go.lyft.com/airflowblog
Icons under Creative Commons License from https://thenounproject.com/ 43

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Backup
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