ML Platform Q1 Meetup: Airbnb's End-to-End Machine Learning Infrastructure

Bighead
Airbnb’s End-to-End Machine
Learning Infrastructure
Krishna Puttaswamy & Nick Handel
On behalf of ML Infra @ Airbnb

In 2016
● Only major models in production
● Models took on average 8 weeks to build (source: survey of ML producers)
● Everything built in Aerosolve, Spark and Scala
● No support for Tensorflow, PyTorch, SK-Learn or other popular ML packages
● Significant discrepancies between offline and online data
ML Infra was formed with the charter to:
● Enable more users to build ML products
● Reduce time and effort
● Enable easier model evaluation
Q4 2016: Formation of our ML Infra team

Before ML
Infrastructure
ML has had a massive impact on Airbnb’s
product
● Search Ranking
● Smart Pricing
● Trust
● Paid Growth
● …And a few other major models

After ML
Infrastructure
But there were many other areas that had
high-potential for ML, but were realized less of
that potential.
● Paid Growth - Hosts
● Classifying listing
● Experience Ranking + Personalization
● Host Availability
● Business Travel Classifier
● Room Type Categorizations
● Make Listing a Space Easier
● Customer Service Ticket Routing
● … And many more

Vision
Airbnb routinely ships ML-powered features throughout the
product.
Mission
Equip Airbnb with shared technology to build
production-ready ML applications with no incidental
complexity.
(Technology = tools, platforms, knowledge, shared feature data, etc.)

Value of ML
Infrastructure
Machine Learning Infrastructure can:
● Remove incidental complexities, by providing
generic, reusable solutions
● Simplify the workflow for intrinsic
complexities, by providing tooling, libraries,
and environments that make ML
development more efficient
And at the same time:
● Establish a standardized platform that
enables cross-company sharing of feature
data and model components
● “Make it easy to do the right thing” (ex:
consistent training/streaming/scoring logic)

Learnings:
● No consistency between ML Workflows
● New teams struggle to begin using ML
● Airbnb has a wide variety in ML applications
● Existing ML workflows are slow, fragmented, and brittle
● Incidental complexity vs. intrinsic complexity
● Build and forget - ML as a linear process
Q1 2017: Figuring out what to build

● Consistent environment across the stack
○ Use Docker
● Common workflow across different ML frameworks
○ Supports Scikit-learn, TF, PyTorch, etc.
● Modular components
○ Easy to customize parts
○ Easy to share data/pipelines
Key Design Decisions

Components
air/mlinfravision
● Data Management: Zipline
● Training: Redspot / BigQueue
● Core ML Library: Bighead libraries
● Productionization: Deep Thought (online) / ML Automator (offline)
● Model Management: Model Repo
● Monitoring: Model Repo UI

Zipline (ML Data Management Framework)

Zipline - Why
● Defining features (especially windowed) with hive was complicated and error
prone
● Backfilling training sets (on inefficient hive queries) was a major bottleneck
● No feature sharing
● Inconsistent offline and online datasets
● Warehouse is built as of end-of-day, lacked point-in-time features
● ML data pipelines lacked data quality checks or monitoring
● Ownership of pipelines was in disarray

A data management platform for ML
● Common (and simple) definition: Define the feature once and use it in batch
and streaming
● Training data backfills: Resource efficient and point-in-time correct with
scheduled updates
● Lambda updates: Features available both offline and online
● Data quality: Feature visualizations and automatic data quality monitoring
Zipline - Overview

Zipline - Feature definition language
Primary Key
Timestamp
Owner
Operation = Sum
Time windows
● Owner allows us
to trace
accountability
● Primary keys and
timestamp are
used to guarantee
point in time
correctness in
Training Set
● Operations and
time windows are
optional
● Spark efficiently
handles
aggregations
(windowed and
not)

Zipline - Data Quality and Collaboration
● Features can be
visualized and
browsed through
online editor
● Gives stats on
feature, and also
provides info on
ownership

Zipline - Training Data
PK1 = User ID PK2 = Listing ID Timestamp bookings_by_user bookings_by_listing
123 456 2018-01-01 23... 0 4
234 567 2018-01-04 01... 2 8
456 789 2018-01-02 08... 1 0
User provides: Primary keys, timestamps, list of features
Zipline computes feature values
point-in-time correct for those PKs and
those timestamps. And joins them
together.
FeatureSet 1 FeatureSet 2

Zipline - Training Data
Airflow integration for daily
update of training data

Label logic
● Labels are often
joined to features with
an offset for training
(60 days offset)
● But that offset does
not apply to scoring
data
Zipline - Training Data with Labels
ds=2017-08-16
ds=2017-10-15
???
Features Table Labels Table
Training
...
???
ds=2017-10-15
Scoring

Features served
from online KV
store
Zipline schedules
daily batch
correction
Zipline - Consistent online and offline features
User writes one conf
Zipline starts the
streaming job

● More efficient cluster usage: Hive and Spark jobs are optimized; Many weeks
to create training data backfills => a few hours
● Ease of use: Can define 100s of new features in a few hours (from many days)
● Online scoring with lambda: Features are automatically availability in online
scoring environment
● Collaboration: Many features are shared!
● Management: Clear data ownership and maintenance
Zipline - Impact

Redspot (Hosted Jupyter Notebook Service)

● Started with Jupyterhub (open-source project), which manages multiple Jupyter
Notebook Servers (prototyping environment)
● But users were installing packages locally, and then creating virtualenv for
other parts of our infra
○ Environment was very fragile
● Users wanted to be able to use jupyterhub on larger instances or instances
with GPU
● Wanting to share notebooks with other teammates was common too
Redspot - Why

Containerized environments
● Every user’s environment is containerized via docker
○ Allows customizing the notebook environment without
affecting other users
■ e.g. install system/python packages
○ Easier to restore state therefore helps with reproducibility
● Support using custom docker images
○ Base images based on user’s needs
■ e.g. GPU access, pre-installed ML packages
○ Build your own image for a faster start time

Remote Instance Spawner
● For bigger jobs and total isolation,
Redspot allows launching a dedicated
instance
● Hardware resources not shared with
other users
● Automatically terminates idle instances
periodically

● A multi-tenant notebook environment
● Makes it easy to iterate and prototype ML models, share work
○ Integrated with the rest of our infra - so one can deploy a notebook to prod
● Improved upon open source Jupyterhub
○ Containerized; can bring custom Docker env
○ Remote notebook spawner for dedicated instances (P3 and X1 machines on
AWS)
○ Persist notebooks in EFS and share with teams
○ Reverting to prior checkpoint
Redspot Summary

Deep Thought (Online Inference Service)

● Performant, scalable execution of model inference in production is hard
○ Engineers shouldn’t build one off solutions for every model.
○ Data scientists should be able to launch new models in production with minimal
eng involvement.
● Debugging differences between online inference and training are difficult
○ We should support the exact serialized version of the model the data scientist
built
○ We should be able to run the same python transformations data scientists write
for training.
○ We should be able to load data computed in the warehouse or streaming easily
into online scoring.
Deep Thought - Why

● Deep Thought is a shared service for online inference
○ Support for pickled sklearn models, TensorFlow models, and custom code in
python or Java
○ Add your model configuration to a file and deploy. Completely config driven so data
scientists don’t have to involve engineers to launch new models.
○ Engineers can then connect to a REST API from other services to get scores.
○ Support for loading data from K/V stores
○ Standardized logging, alerting and dashboarding for monitoring and offline
analysis of model performance
○ Process isolation to enable multi-tenancy without contention
○ Scalable and Reliable: 80+ models. Highest QPS service at Airbnb. Median response
time: 4ms. p95: 13ms.
Deep Thought - How

Model Repo
Overview
Model Repo is Bighead’s model management service
● Contains prototype and production models
● Can serve models “raw” or trained
● The source of truth on which trained models are
in production
● Stores model health data

Model Repo
Internals
We decompose Models into two components:
● Model Version - raw model code + docker image
● Model Artifact - parameters learned via training
Model
Version
Model Artifact
Code
Docker
Image
A trained model consists of:
Model Version
+
Model Artifact
Production

Our built-in UI provides:
● Deployment - review changes, deploy, and rollback trained models
● Model Health - metrics, visualizations, alerting, central dashboard
● Experimentation - Ability to setup model experiments - e.g. split traffic
between two or more models
Model Repo: UI

● Tools and libraries for common tasks
○ Periodic training, evaluation and scoring on a model is common: Building Airflow
DAGs, uploading scores to K/V stores, dashboards on scores, alert on score changes
○ Scoring on large tables is tricky to scale
ML Automator - Why

● Once a model file is checked in, we generate the DAGs automatically to train/score it
● 40+ models using this feature
● Score on Spark for large datasets (we generate virtualenv equivalent to the docker image,
as spark doesn’t run executors in docker image)
ML Automator

ML Helpers - Why
● Transformations are re-written too often
○ There are many versions of transformations for NLP, data cleaning, imputing, etc.
○ Models used to “start from scratch” and rebuild the same things
○ Model observability -- understand what features are important

● Library of transformations; holds more than 50 different transformations including
automated preprocessing for common input formats
● Created example notebooks to show usage of our infra
○ Example usage of ML pipelines, contains diagnostics that help people debug and
improve models
○ Has been cloned and modified more than 20 times to build new models
● Improved Scikit-Learn Pipelines
○ Propagate feature metadata so we can plot feature importance at the end and
connect it to feature names
○ Pipelines for data processing are reusable in other pipelines
○ Added wrappers for model libraries (XGB, etc.) can be serialized (robust to minor
version changes)
ML Helpers and Pipelines

Open Source in H1 2018
If you want to collaborate we can provide
early access
nick.handel@airbnb.com
krishna.puttaswamy@airbnb.com

ML models have diverse dependency sets (tensorflow,
xgboost, etc.). We allow users to provide a docker image
within which model code always runs.
ML models don’t run in isolation however, so we’ve built a
lightweight API to interact with the “dockerized model”
Docker Container
Model
(user code)
Other ML
Infra
Services
Model
API
Dockerized
Models

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