The Stack That Helped Opendoor Buy and Sell Over $1B in Homes

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Opendoor
A new way to buy and sell homes. Opendoor allows homeowners to sell their home online in a few clicks, bringing certainty and simplicity to what is usually a long and stressful process.

By Alex Zirbel, Software Engineer at Opendoor.


About Opendoor

Unless you’re in San Francisco or New York, selling your home is a giant headache that typically lasts three months. Opendoor removes the headache — go online, ask for an offer, answer a few questions and we’ll buy your home directly from you. We’ll take it from there and deal with selling the home to another buyer while you can go on with your life.

Right now we operate in Phoenix, Dallas, and Las Vegas. We’ve completed over 4,800 real estate transactions — over $1B in homes. For a company about to turn 3 years old, it’s pretty crazy how far we’ve come.

There’s a lot that goes into one real estate transaction. First, there’s what you might consider our core engineering challenge: making an accurate offer on each home. If we offer too much, we’ll lose money and go out of business; if we offer too little, we’ll seem like scammers and offend our customers.

After we buy the home, we’ll work with contractors to do any necessary repairs and touch-ups, then put the home on the market and find a buyer. Since we own every home, we can do clever things like putting smart locks on all the doors and offering all-day open houses.



I’m a frontend engineer, and mainly like to work on the consumer-facing website. I’m currently working on improving the experience for first-time home buyers. The process can be really scary for people who don’t know anything about real estate.

Engineering Organization

Our team is split between product engineering and data science: the tools used by each team are different enough that the teams work in separate code bases. Of course, the resulting product has to be well-integrated, and the product team pulls a lot of data from data science APIs. This coordination is tricky to get right; Kevin Teh from the data science team wrote about it in some detail in a recent post.

At first, we split the product team into “customer-facing” and “internal tools” groups. It was nice to have all the frontend engineers on the same team, but we noticed that some projects didn’t have clear owners. For example, our buyer support team uses some internal tools we’ve built. Should those tools be developed by the “internal tools” team, or is support part of the customer experience?

Now the team is split into cross-functional teams based around parts of the business. The Seller team handles people selling to us; the Homes team handles renovations and inventory; and the Buyer team puts our homes on the market and finds buyers.

As we grow, the lines between teams often get blurry, so we expect that the structure will always be evolving. It’s common for engineers to move between teams, including between the product and data science teams.

Product Architecture

We started in 2014 with a Ruby on Rails monolith and Angular frontend, both of which were good ways to move fast while we were very small.

The MVP of our customer-facing product was a multi-page form where you could enter information about your home to get an offer, but that was just the tip of the iceberg. We had to build internal tools to help our team correctly price homes and manage the transaction process. We used Angular and Bootstrap to build out those tools; the main goal was to add features quickly, without fiddling around with CSS — in fact, without requiring any frontend experience at all.

We use Puma as our webserver, and Postgres for our database — one big benefit is the PostGIS extension for location data. Sidekiq runs our asynchronous jobs with support from Redis. Elasticsearch shows up everywhere in our internal tools. We use Webpack to build our frontend apps, and serve them using the Rails Asset Pipeline.

We use Imgix to store photos of our homes, as well as most of the icons and illustrations around our site. We mainly use Imgix’s auto-resizing feature, so we never lose track of our original images, but can later load images of appropriate size for each context on the frontend.

Monolith to Microservices

Where appropriate, we try to break isolated logic out into microservices. For example, we’re working on a service which calculates our projected costs and fees. Our cost structure changes frequently, and we want to estimate how policy changes might affect our fees. This code wasn't a great fit for the Rails app because we wanted it to be accessible to our analysts and data scientists as well.

We’ve now split this logic out into its own service. It uses a version-history-aware computation graph to calculate and back-test our internal costs, and (soon!) will come with its own React frontend to visualize those calculations.

Our data science stack is also a fully separate set of services, so there’s a lot of inter-app communication going on. To let these services authenticate to one another, we use an Elixir app called Paladin. Opendoor engineer Dan Neighman wrote and open-sourced Paladin, and explains why it’s helpful in this blog post. Authentication is based on JWTs provided by Warden and Guardian.

Data Science Architecture

I’ve always found data science at Opendoor interesting because it’s not the “grab as much data as you possibly can, then process it at huge scale” problem I’m used to hearing about.

To find the price of a house, you look at nearby homes that sold recently, then squeeze as much information out of that data as you possibly can by comparing it to what you know about the market as a whole. Our co-founder Ian Wong has a more in-depth talk here.

We can group most of the data science work into several core areas:

  1. Ingesting and organizing data from a variety of sources
  2. Training machine learning models to predict home value and market risk
  3. Quantifying and mitigating various forms of risk, including macroeconomic and individual house-liquidity
  4. Collecting information in a data warehouse to empower the analytics team

For data ingestion, we pull from a variety of sources (like tax record and assessor data). We dump most of this data into an RDS Postgres database. We also transform and normalize everything at this phase — we’re importing dirty data from sources that often conflict. This blog post goes into more detail on how we merge data for a given address.



For our machine learning model, we use Python with building blocks from SqlAlchemy, scikit-learn, and Pandas. We use Flask for routing/handling requests. We use Docker to build images and Kubernetes for deployment and scaling. Our system lets us describe a model as a JSON configuration, and once deployed, the system automatically grabs the required features, trains the model, and evaluates how well the model did against performance metrics. This automation lets us iterate really fast.

We’re starting to use Dask for feature fetching and processing. Other companies often use Spark and Hadoop for this, but we need support for more complex parallel algorithms. Dask’s comparison to PySpark post describes this perfectly:

Dask is lighter weight and is easier to integrate into existing code and hardware. If your problems vary beyond typical ETL + SQL and you want to add flexible parallelism to existing solutions then dask may be a good fit, especially if you are already using Python and associated libraries like NumPy and Pandas.

The final piece of our data science architecture is the Data Warehouse, which we use to collect analytics data from everywhere we can. For a long time we used a nightly pg_dump to move Postgres data from each service’s database directly into a home-built Data Warehouse. We recently migrated to Google’s BigQuery instead. BigQuery is faster, and lets us fit more data into each query, but the killer feature is that it’s serverless. We have many people running queries at “peak hours”, and don’t want things to slow down just because we have a preallocated number of servers available.

High-Tech Open Houses

Since Opendoor actually owns all the houses we sell, we can be creative about how we show them to potential buyers.

Typically, if you want to see a house for sale, you have to call the listing agent and schedule a time. We realized early on that we could make open houses way more convenient by installing automatic locks on our doors so the homes could be accessed at any time. For version 0 of the project, we literally posted our VP of Product’s phone number on the doors of all our houses — buyers would call in, and he’d tell them the unlock code.

For version 1, we added Twilio so we could automatically send unlock codes over SMS. For version 2, we built a mobile app.



Customers expect a good mobile experience these days, but our all-day open house feature made it twice as important. You can use the app to find nearby homes as you’re driving around, and explore them on a whim — a huge improvement from the traditional process!

We built our app in React Native. A major part of that choice was pragmatic — our team had a lot of experience with web technologies, and almost no experience with native technologies. We also wanted to support both iPhone and Android from early on, and React Native let us do that (we released our app for iPhone first, and adding Android only took an extra couple weeks).

Not everyone wants to install an app, so it's still possible to access our homes via SMS. We’ve added a few security mechanisms — one worth mentioning is Blockscore, which lets us quickly run identity verification using phone numbers. For riskier numbers, we disable the automatic entry system and have our support team call the customer to collect their information.

Tools and Workflows

We manage our repositories and do code reviews on GitHub. All code is reviewed by at least one other engineer, but once it’s in the master branch, it’s assumed to be ready to deploy. If you want to deploy your code, you can do it in three steps:

  1. ./bin/deploy staging
  2. Check your work on staging
  3. ./bin/deploy production

This takes 10-15 minutes in total. We’ve worked hard to automate the process so we can move fast as a team. We use Heroku for hosting, and run automated tests on CircleCI. Slack bots report what’s being deployed.

There are a lot of external services we rely on heavily. To run through them briefly: Help Scout and Dyn for emails; Talkdesk and Twilio for calls and customer service; HelloSign for online contract signing; New Relic and Papertrail for system monitoring; Sentry for error reporting.

For analytics, we’ve used a lot of tools: Mixpanel for the web, Amplitude for mobile, Heap for retroactive event tracking. We mainly use Looker for digging into that data and making dashboards.

Joining Opendoor Engineering

Opendoor has a very entrepreneurial, pragmatic culture: Engineers here typically talk with customers, understand their needs, and take the initiative on projects. We’re big on ownership and empowering others, and are aggressively anti-snark.



We’re looking for engineers of all backgrounds: it doesn’t matter what languages you work with now, we’re sure you’ll ramp up fast.

Find out more about Opendoor jobs on StackShare or on our careers site.

Huge thanks to Kevin Teh, Mike Chen, Nelson Ray, Ian Wong, and Alexey Komissarouk for their help putting together this post.

Opendoor
A new way to buy and sell homes. Opendoor allows homeowners to sell their home online in a few clicks, bringing certainty and simplicity to what is usually a long and stressful process.
Tools mentioned in article
Open jobs at Opendoor
Engineering Manager - Los Angeles
Los Angeles, CA
About Opendoor Are you intrigued by the thought of disrupting a trillion dollar industry through technology? At Opendoor, we are on a bold mission to empower everyone with the freedom to move by making buying, selling and trading-in a home stress-free and instant. In four years since we started, we have hired an exceptional team, seen strong growth, bought and sold over 20,000 homes (with an annual purchase run rate exceeding $3.8 billion), and raised over $1 billion in equity funding. The coming years present a tremendous opportunity for innovation as we explore new frontiers and scale nationwide. We're looking for an Engineering Manager who will lead, manage, and inspire the engineering team to build the future of real estate. You'll help us build on our current culture of high performance where outstanding, diverse engineers can succeed. As an Engineering Manager, you'll be integral in growing the team by recruiting and hiring exceptional candidates.
  • Lead engineering team members in growing their technical and non-technical skills through hands-on management.
  • Guide the team to deliver technical solutions to achieve business goals. Unblock the team and focus the engineers on building the right solutions to deliver customer value.  
  • Consistently raise the bar for engineering practices and culture: advocate for best practices and lead by example.  Continuously examine and improve our software development processes.  Take freely from agile and be flexible and data-driven in introducing changes. 
  • Help keep work moving through the engineering pipeline, write code reviews, check for appropriate test coverage, create acceptance criteria, and help engineers release features.  You’ll also communicate feature launches to the organization at large.
  • Continue to grow the engineering team by identifying important roles to fill and recruiting and hiring exceptional candidates. 
  • Actively contribute to our product strategy.
  • 6 years or more experience as a manager of software engineers.
  • A solid background in software development. Expertise in JavaScript and/or Ruby.
  • Experience shipping scalable applications with robust architectural patterns.
  • A strong will to advocate for testing and belief that appropriate testing reduces total engineering time.
  • A demonstrable record of helping your team members learn, grow, and achieve. 
  • You love delighting customers with honest, transparent products and experiences
  • Domain knowledge and/or interest in real estate
  • Competitive salary & benefits
  • 100% free health, dental and vision insurance
  • Equity in a YC-backed, VC-funded startup
  • Chill hillside office in sunny Silver Lake, Los Angeles
  • Positive, balanced, flexible vibes
  • Software Engineer (Mobile) - Los Angeles
    Los Angeles, CA
    About Opendoor Are you intrigued by the thought of disrupting a trillion dollar industry through technology? At Opendoor, we are on a bold mission to empower everyone with the freedom to move by making buying, selling and trading-in a home stress-free and instant. In four years since we started, we have hired an exceptional team, seen strong growth, bought and sold over 20,000 homes (with an annual purchase run rate exceeding $3.8 billion), and raised over $1 billion in equity funding. The coming years present a tremendous opportunity for innovation as we explore new frontiers and scale nationwide. Today, our software plugs into the existing real estate market via broker-quality data feeds and a network of local real estate agents. We have a web/app feed that helps users house hunt, back-of-house software that helps agents manage transactions, and custom support tools that allow our small team to assist thousands of active buyers through the process. We take a pragmatic, piecemeal approach to crafting software with heavy emphasis on testing, measurement, and iteration. The Role As a mobile developer, you'll work on the Opendoor app, written in React Native and live today on iTunes and Google Play. We currently use a hybrid approach that uses mobile web views, so you will also work on our React.js web app and the bridge between the two. Specifically, you'll work on initiatives to add new functionality to our app, improve usability, and improve testing. Our strategy includes building native functionality, so experience with native iOS and Android development is a plus.
  • B.S. in Computer Science or equivalent experience
  • Experience building a well-designed app
  • Ability to choose a test-driven approach and write code in a way that lends itself to testing
  • A bias for building your way out of a problem
  • Optimism about future technology and automation
  • Good references from past colleagues
  • You love delighting customers with honest, transparent products and experiences
  • Domain knowledge and/or interest in real estate
  • Competitive salary & benefits
  • 100% free health, dental and vision insurance
  • Equity in a YC-backed, VC-funded startup
  • Chill hillside office in sunny Silver Lake, Los Angeles
  • Positive, balanced, flexible vibes
  • Site Reliability Engineer
    San Francisco, CA
    About Opendoor Are you intrigued by the thought of disrupting a trillion dollar industry through technology? At Opendoor, we are on a bold mission to empower everyone with the freedom to move by making buying, selling and trading-in a home stress-free and instant. In four years since we started, we have hired an exceptional team, seen strong growth, bought and sold over 20,000 homes (with an annual purchase run rate exceeding $3.8 billion), and raised over $1 billion in equity funding. The coming years present a tremendous opportunity for innovation as we explore new frontiers and scale nationwide. Site Reliability Engineering (SRE) at Opendoor fills the mission-critical role of ensuring that our monolith and micro services are healthy, monitored, automated, and designed to scale. You will use your background as an operations generalist to work closely with our development teams from the early stages of design all the way through identifying and resolving production issues that relate to infrastructure. The ideal candidate will be passionate about an operations role that involves deep knowledge of both the application and the product, and will also believe that automation is a key component to operating our monolith and micro services in a Kubernetes compute environment. We’re looking for a talented Site Reliability Engineer to join our Platform Engineering team. You will work closely with developers and engineering managers from the developer experience team as well as product facing engineering teams. 
  • Keep the customer-facing services available at top performance by maintaining the constant health of the supporting systems.
  • Act in key support roles during major incidents e.g. Sev0, Sev1. Also, participate in the technical review of the incident for problem management.
  • Develop tools to improve our ability to rapidly deploy and effectively monitor web services in a containerized environment.
  • Work closely with development teams to ensure that platforms are designed with"operability" in mind.
  • 4+ years of experience with operating web services in a production environment.
  • Good scripting ability with Bash, Python, Ruby, or Perl.
  • Experience with monitoring systems such as datadog, or other open source monitoring solutions.
  • Moderate experience with TCP/IP networking.
  • Practical experience managing databases or search engines, such as Postgres, MySQL, Oracle, Cassandra or ElasticSearch.
  • Ability to work independently with minimal supervision.
  • Ability to participate in a 24/7 on-call rotation.
  • Unwavering commitment to operational security and best practices.
  • Function well in a fast-paced, rapidly-changing environment.
  • BS/MS in Computer Science
  • Experience with container platforms such as Kubernetes, Mesos 
  • Knowledge of server hardware and/or experience working with Amazon Web Services(AWS)
  • Senior React Native Engineer - Los An...
    Los Angeles, CA
    About Opendoor Are you intrigued by the thought of disrupting a trillion dollar industry through technology? At Opendoor, we are on a bold mission to empower everyone with the freedom to move by making buying, selling and trading-in a home stress-free and instant. In five years since we started, we have hired an exceptional team, seen strong growth, bought and sold over 20,000 homes (with an annual purchase run rate exceeding $3.8 billion), and raised $1.3 billion in funding. The coming years present a tremendous opportunity for innovation as we explore new frontiers and scale nationwide. Today, our software plugs into the existing real estate market via broker-quality data feeds and a network of local real estate agents. We have a web/app feed that helps users house hunt, back-of-house software that helps agents manage transactions, and custom support tools that allow our small team to assist thousands of active buyers through the process. We take a pragmatic, piecemeal approach to crafting software with heavy emphasis on testing, measurement, and iteration. As a Senior Mobile Engineer, you will work on the Opendoor app, written in React Native and live today on iTunes and Google Play.  In addition, you will lead the technical direction, architecture and implementation of our mobile app, collaborate with product managers and designers to understand complex requirements, promote software development best practices, and mentor other engineers.  An ideal candidate for this role will have a demonstrated ability to deliver results, high attention to detail, team-player mindset, and curiosity to keep learning Our stack is Rails, React.js, React Native, and MongoDB, with a heavy peppering of AWS goodies. The only tool we’re dogmatic about is simplicity. You should be comfortable developing the full critical path of a new web feature, but we’re most excited about front end web and/or native app expertise.
  • Experience building scalable React Native apps
  • Cross functional collaboration with other eng. teams to build modular / reusable react native components
  • Provide technical leadership in determination of current limitations and proposing solutions to ensure we’re building for the future
  • Raise the bar for technical standards, performance, reliability, and overall code quality
  • Experience with REST APIs
  • Play an active role in hiring, mentoring and career development of other engineers
  • B.S. in Computer Science or equivalent experience
  • 5+ years of industry experience
  • Minimum of 1 year working with React Native
  • Experience building a well-designed app
  • A bias for building your way out of a problem
  • Get things done attitude
  • Optimism about future technology and automation
  • Good references from past colleagues
  • A sense of ownership and a passion for delighting customers through innovation and simple solutions to complex problems
  • You love delighting customers with honest, transparent products and experiences
  • Domain knowledge and/or interest in real estate
  • Experience with GraphQL
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