Khan Engineering

Khan Engineering

We're the engineers behind Khan Academy. We're building a free, world-class education for anyone, anywhere.

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Latest posts

How Khan Academy Successfully Handled 2.5x Traffic in a Week

Marta Kosarchyn on May 9

Go + Services = One Goliath Project

Kevin Dangoor on Dec 20, 2019

How to upgrade hundreds of React components without breaking production

Jangmi Jo on Sep 23, 2019

How Engineering Principles Can Help You Scale

Marta Kosarchyn on Aug 21, 2019

Making Websites Work with Windows High Contrast Mode

Diedra Rater on Mar 21, 2019

Kotlin for Python developers

Aasmund Eldhuset on Nov 29, 2018

Using static analysis in Python, JavaScript and more to make your system safer

Kevin Dangoor on Jul 26, 2018

Kotlin on the server at Khan Academy

Colin Fuller on Jun 28, 2018

The Original Serverless Architecture is Still Here

Kevin Dangoor on May 31, 2018

What do software architects at Khan Academy do?

Kevin Dangoor on May 14, 2018

New data pipeline management platform at Khan Academy

Ragini Gupta on Apr 30, 2018

Untangling our Python Code

Carter J. Bastian on Apr 16, 2018

Slicker: A Tool for Moving Things in Python

Ben Kraft on Apr 2, 2018

The Great Python Refactor of 2017 And Also 2018

Craig Silverstein on Mar 19, 2018

Working Remotely

Scott Grant on Oct 2, 2017

Tips for giving your first code reviews

Hannah Blumberg on Sep 18, 2017

Let's Reduce! A Gentle Introduction to Javascript's Reduce Method

Josh Comeau on Jul 10, 2017

Creating Query Components with Apollo

Brian Genisio on Jun 12, 2017

Migrating to a Mobile Monorepo for React Native

Jared Forsyth on May 29, 2017

Memcached-Backed Content Infrastructure

Ben Kraft on May 15, 2017

Profiling App Engine Memcached

Ben Kraft on May 1, 2017

App Engine Flex Language Shootout

Amos Latteier on Apr 17, 2017

What's New in OSS at Khan Academy

Brian Genisio on Apr 3, 2017

Automating App Store Screenshots

Bryan Clark on Mar 27, 2017

It's Okay to Break Things: Reflections on Khan Academy's Healthy Hackathon

Kimerie Green on Mar 6, 2017

Interning at Khan Academy: from student to intern

Shadaj Laddad on Dec 12, 2016

Prototyping with Framer

Nick Breen on Oct 3, 2016

Evolving our content infrastructure

William Chargin on Sep 19, 2016

Building a Really, Really Small Android App

Charlie Marsh on Aug 22, 2016

A Case for Time Tracking: Data Driven Time-Management

Oliver Northwood on Aug 8, 2016

Time Management at Khan Academy

Several Authors on Jul 25, 2016

Hackathons Can Be Healthy

Tom Yedwab on Jul 11, 2016

Ensuring transaction-safety in Google App Engine

Craig Silverstein on Jun 27, 2016

The User Write Lock: an Alternative to Transactions for Google App Engine

Craig Silverstein on Jun 20, 2016

Khan Academy's Engineering Principles

Ben Kamens on Jun 6, 2016

Minimizing the length of regular expressions, in practice

Craig Silverstein on May 23, 2016

Introducing SwiftTweaks

Bryan Clark on May 9, 2016

The Autonomous Dumbledore

Evy Kassirer on Apr 25, 2016

Engineering career development at Khan Academy

Ben Eater on Apr 11, 2016

Inline CSS at Khan Academy: Aphrodite

Jamie Wong on Mar 29, 2016

Starting Android at Khan Academy

Ben Komalo on Feb 29, 2016

Automating Highly Similar Translations

Kevin Barabash on Feb 15, 2016

The weekly snippet-server: open-sourced

Craig Silverstein on Feb 1, 2016

Stories from our latest intern class

2015 Interns on Dec 21, 2015

Kanbanning the LearnStorm Dev Process

Kevin Dangoor on Dec 7, 2015

Forgo JS packaging? Not so fast

Craig Silverstein on Nov 23, 2015

Switching to Slack

Benjamin Pollack on Nov 9, 2015

Receiving feedback as an intern at Khan Academy

David Wang on Oct 26, 2015

Schrödinger's deploys no more: how we update translations

Chelsea Voss on Oct 12, 2015

i18nize-templates: Internationalization After the Fact

Craig Silverstein on Sep 28, 2015

Making thumbnails fast

William Chargin on Sep 14, 2015

Copy-pasting more than just text

Sam Lau on Aug 31, 2015

No cheating allowed!!

Phillip Lemons on Aug 17, 2015

Fun with slope fields, css and react

Marcos Ojeda on Aug 5, 2015

Khan Academy: a new employee's primer

Riley Shaw on Jul 20, 2015

How wooden puzzles can destroy dev teams

John Sullivan on Jul 6, 2015

Babel in Khan Academy's i18n Toolchain

Kevin Barabash on Jun 22, 2015

tota11y - an accessibility visualization toolkit

Jordan Scales on Jun 8, 2015

Meta

How Khan Academy Successfully Handled 2.5x Traffic in a Week

by Marta Kosarchyn on May 9

Talk about rapid scaling...

A few months ago I posted some thoughts on scaling and promised to post more soon. Well, talk about rapid scaling — within just two weeks in March, Khan Academy site usage grew to 2.5x what it was at the same time last year and has sustained that level to date. As schools all over the world closed because of the coronavirus pandemic and students, parents, and teachers moved to distance learning, Khan Academy was able to respond, offering high-quality content and classroom experience — for free. In the month of April, we served 30 million learners on our platform. A recent national survey of parents found that Khan Academy was the “most used online resource”.

I’m proud that we absorbed this rapid growth without disrupting our users. In addition to reacting quickly to alleviate pressure points within a few days, we had prepared in advance, and that preparation paid dividends. We scaled readily in large part because of our architecture and a rigorous practice of choosing external services carefully and using them properly.

So in this post I’ll discuss architectural aspects that play a key role in the scalability of our site.

Two fundamental components of our architecture serve us particularly well here. We use Google Cloud, including AppEngine, Datastore, and Memcache, and Fastly CDN, and they were the backbone of the serverless and caching strategy that’s key to our scalability.

Architecture Diagram

Serverless infrastructure

Using GCP App Engine, a fully managed environment, means we can scale very easily with virtually no effort. Even with a substantial traffic increase, our site stayed up and performed well, with minimal intervention. We didn’t need to worry about load balancing ourselves because server instances were brought up as needed without any intervention. We similarly use Datastore which scales out storage and access capacity automatically in much the same way App Engine scales out web server instances.

Caching

Fastly CDN allows us to cache all static data and minimize server trips. Huge for scalability, it also helps us optimize hosting resources, for which costs grow linearly with usage in our App Engine serverless model. As shown in the architecture diagram, all client requests go through Fastly so we can prevent unnecessary server traffic, improving performance. We load videos primarily from YouTube and secondarily from Fastly. This also keeps costs down as well as ensures that the videos load quickly.

In addition to caching static data in Fastly, we also extensively cache common queries, user preferences, and session data, and leverage this to speed up data fetching performance. We use Memcache liberally, in addition to exercising other key best practices around Datastore to ensure quick response times.

Our site reliability (SRE) team of course needed to be prepared with ironclad monitoring - and we were. We noticed some slowdowns in the first few days and found that deploys were causing those hits. At our request, Google increased our Memcache capacity, and within a week we were comfortable returning to our normal continuous deployment pattern. This speed was critical, as our teams were quickly developing resources to guide new site users in onboarding as easily as possible.

Overall, we work hard to choose services carefully, follow best practices, and develop our own as needed. With the right technology, careful preparation, and adjustments on the spot by our amazing engineering team, we’ve been able to serve the students, parents, and teachers who rely on us now more than ever without interruption.


Khan Academy's increased usage has also increased our hosting costs, and we're a not-for-profit that relies on philanthropic donations from folks like you.