E-Commerce at Scale: Inside Shopify's Tech Stack

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Sz2gvpcj
Shopify
Shopify powers tens of thousands of online retailers including General Electric, Amnesty International, CrossFit, Tesla Motors, Encyclopaedia Britannica, Foo Fighters, GitHub, and more. Our platform allows users to easily and quickly create their own online store without all the technical work involved in developing their own website, or the huge expense of having someone else build it. Shopify lets merchants manage all aspects of their shops: uploading products, changing the design, accepting credit card orders, and viewing their incoming orders and completed transactions.

Written by Kir Shatrov, Production Engineer at Shopify


Background

Shopify is a multi-channel commerce platform for small and medium businesses that lets you create a shop and sell products wherever you want: online via web store or social media and offline with a POS card reader. Shopify powers 600K merchants and serves 80K requests per second at peak.

While helping aspiring entrepreneurs to launch their stores, Shopify also holds some of the world's largest sales for the Super Bowl, Kylie Cosmetics, and celebrities like Justin Bieber and Kanye West. These "flash sales" are tricky from an engineering point of view because of their unpredictably large volumes of traffic.

My name is Kir Shatrov and I'm a Senior Production Engineer at Shopify working on the Service Patterns team. Our team owns areas like sharding, scalability and reliability of the platform. We provide guidelines and APIs on how to write software that scales by default, which essentially makes the rest of developers at Shopify our customers. Our team's motto is "make scale invisible for developers".


Engineering at Shopify

Before 2015, we had an Operations and Performance team. Around this time, we decided to create the Production Engineering department and merge the teams. The department is responsible for building and maintaining common infrastructure that allows the rest of product development teams to run their code.

Both Production Engineering and all the product development teams share responsibility for the ongoing operation of our end user applications. This means all technical roles share monitoring and incident response, with escalation happening laterally to bring in any skill set required to restore service in case of problems.


Initial architecture and stack

In 2004, Shopify’s CEO and founder, Tobi Lütke, was building out an e-commerce store for snowboarding products. Unsatisfied with the existing e-commerce products on the market, Tobi decided to build his own SaaS platform using Ruby on Rails.

At that time, Rails wasn't even 1.0 yet, and the only version of the framework was exchanged as a .zip archive by email. Tobi joined Rails creator David Heinemeier Hansson (DHH) and started contributing to Ruby on Rails while building Shopify.

Shopify is now one of the world's largest and oldest Rails apps. It’s never been rewritten and still uses the original codebase, though it has matured considerably over the past decade. All of Tobi’s original commits are still in the version control history.

The bet on Rails greatly shaped how we think at Shopify and empowered us to deliver product as fast as possible. While there are parts of the framework that sometimes make it harder to scale (e.g. ActiveRecord callbacks and code organization), many of us tend to agree with Tobi that Rails is what allowed Shopify to move from a garage startup to a public company.

The core Shopify app has remained a Rails monolith, but we also have hundreds of other Rails apps across the organization. These are not microservices, but domain-specific apps: Shipping (talks with various shipping providers), Identity (single sign on across all Shopify stores), and App Store to name a few. Managing a hundred apps and keeping them up to date with security updates can be tough, so we've developed ServicesDB, an internal app that keeps track of all production services and helps developers to make sure that they don't miss anything important.


ServicesDB ServicesDB in Action


ServicesDB keeps a checklist for each app: ownership, uptime, logs, on-call rotation, exception reporting, and gem security updates. If there are problems with any of those, ServicesDB opens a GitHub issue and pings owners of the app to ask them to address it. ServicesDB also makes it easy to query the infrastructure and answer questions like, “How many apps are on Rails 4.2? How many apps are using an outdated version of gem X? Which apps are calling this service?”.


Our current stack

As is common in the Rails stack, since the very beginning, we've stayed with MySQL as a relational database, memcached for key/value storage and Redis for queues and background jobs.


Shopify Rails Stack


In 2014, we could no longer store all our data in a single MySQL instance - even by buying better hardware. We decided to use sharding and split all of Shopify into dozens of database partitions.

Sharding played nicely for us because Shopify merchants are isolated from each other and we were able to put a subset of merchants on a single shard. It would have been harder if our business assumed shared data between customers.

The sharding project bought us some time regarding database capacity, but as we soon found out, there was a huge single point of failure in our infrastructure. All those shards were still using a single Redis. At one point, the outage of that Redis took down all of Shopify, causing a major disruption we later called “Redismageddon”. This taught us an important lesson to avoid any resources that are shared across all of Shopify.

Over the years, we moved from shards to the concept of "pods". A pod is a fully isolated instance of Shopify with its own datastores like MySQL, Redis, memcached. A pod can be spawned in any region. This approach has helped us eliminate global outages. As of today, we have more than a hundred pods, and since moving to this architecture we haven't had any major outages that affected all of Shopify. An outage today only affects a single pod or region.


Shopify Pods Architecture


As we grew into hundreds of shards and pods, it became clear that we needed a solution to orchestrate those deployments. Today, we use Docker, Kubernetes, and Google Kubernetes Engine to make it easy to bootstrap resources for new Shopify Pods. On the load balancer level we leverage Nginx, Lua and OpenResty which allow us to write scriptable load balancers.

The client-side stack of Shopify Admin has been a long journey. It started with HTML templates, jQuery and prototype.js. We moved to Batman.js, our in-house Single-Page-Application framework (SPA), in 2013. Then, we re-evaluated our approach and moved back to statically rendered HTML and vanilla JavaScript. As the front-end ecosystem matured, we felt that it was time to rethink our approach again. Last year, we started working on moving Shopify Admin to React and TypeScript.

Many things have changed since the days of jQuery and Batman. JavaScript execution is much faster. We can easily render our apps on the server to do less work on the client, and the resources and tooling for developers are substantially better with React than we ever had with Batman.

Another very notable difference is that now we have a much better solution for ensuring business logic does not leak into the client — GraphQL. The Admin becomes just another GraphQL client and follows the same patterns established by the mobile apps: no data persistence, no reliance on the server for anything that needs to be shared between clients, and extremely efficient fetching of resources for a view.


How we build, test, and deploy

The Shopify monolith has around 100K unit tests. Many of those involve heavy ORM calls, so they aren't very fast. To keep the shipping pipeline fast, we've massively invested in our CI infrastructure.

We use BuildKite as a CI platform. What makes BuildKite unique is that it lets you run tests in your own way, on your own hardware while BuildKite orchestrates builds and provides user interface.


Shopify BuildKite


The build of our monolith takes 15-20 minutes and involves hundreds of parallel CI workers to run all 100k tests. Parallel test workers allow us to keep shipping. Otherwise, a single build could take days. We have hundreds of developers shipping new features and improvements every day, and it’s crucial that we keep the continuous integration pipeline fast.

When the build is green, it's time to deploy changes to production. We don't practice staging or canary deploys, instead we rely on feature flags and fast rollbacks in case something goes wrong.


Shopify ShipIt Engine


ShipIt, our deployment tool, is at the heart of Continuous Delivery at Shopify. ShipIt is an orchestrator that runs and tracks progress of any deploy script that you provide for a project. It supports deploying to Rubygems, Pip, Heroku and Capistrano out of the box. For us, it's mostly kubernetes-deploy or Capistrano for legacy projects.


Shopify ShipIt Slack A ShipIt Slack notification sent when your code is being deployed


We use a slightly tweaked GitHub flow, with feature development going in branches and the master branch being the source of truth for the state of things in production. When your PR is ready, you add it to the Merge Queue in ShipIt. The idea behind the Merge Queue is to control the rate of code that is being merged to master branch. In the busy hours, we have many developers who want to merge the PRs, but at the same time we don't want to introduce too many changes to the system at the same time. Merge Queue limits deploys to 5-10 commits at a time, which makes it easier to identify issues and roll back in case we notice any unexpected behaviour after the deploy.

We use a browser extension to make Merge Queue play nicely with the Merge button on GitHub:


Shopify GitHub flow


Both ShipIt and kubernetes-deploy are open source, and we've heard quite a few success stories from companies who have adopted our flow.


Next Challenges

All systems at Shopify have to be designed with the scale in mind. At the same time, it still feels like you're working on a classic Rails app. The amount of engineering efforts put into this is incredible. For a developer writing a database migration, it looks just like it would for any other Rails app, but under the hood that migration would be asynchronously applied to a 100+ database shards with zero downtime. This story is similar for any other aspect of our infrastructure, from CI and tests to deploys.

In Production Engineering, we've put a lot of efforts to migrate our infrastructure to Kubernetes. Some approaches and design decisions had to be evaluated as they were not ready for cloud environments. At the same time, many of those investments into Kubernetes have already started to pay off. What took me days of writing Chef cookbooks before, now is a matter of a couple of changes in Kubernetes' YAML. I expect that our Kubernetes foundation will mature, and unlock us even more possibilities to scale.

With tools like Semian and Toxiproxy, we've done great job at shaping our monolith towards high reliability and resiliency. At the same time, we’re approaching one hundred other production services running at the company — most of them using Rails. With a tool like ServicesDB, we can verify that all of them are using the same patterns as the monolith, spreading the lessons we learned from a decade of operating Rails apps at scale.

Many of these services also need to talk to each other in some way, and how they do it is currently up to them. Some services communicate via a message log like Kafka and some use a REST API over HTTP. Lately, we've been looking into options for Shopify-wide RPC and Service Mesh. I expect that over the next year, we'll define how applications will communicate on our platform in a way that will be resilient and scalable by default.


Like the sound of this stack? Shopify is hiring. Come help us to make commerce better for everyone. Or join Production Engineering, and help us continue to evolve the stack that makes commerce better at Shopify than anywhere else in the world.

Sz2gvpcj
Shopify
Shopify powers tens of thousands of online retailers including General Electric, Amnesty International, CrossFit, Tesla Motors, Encyclopaedia Britannica, Foo Fighters, GitHub, and more. Our platform allows users to easily and quickly create their own online store without all the technical work involved in developing their own website, or the huge expense of having someone else build it. Shopify lets merchants manage all aspects of their shops: uploading products, changing the design, accepting credit card orders, and viewing their incoming orders and completed transactions.
Launch Engineer - Shopify Plus (Ontario)
Ontario, Canada - Remote
Shopify Plus is making enterprise commerce simple. We give high growth, high volume merchants the scalability, reliability and flexibility they need. Shopify Plus is helping power commerce for companies like, RedBull, GE, Beastmode, Nine West, Kanye West, Kylie Cosmetics, and many more. We believe large merchants should love their commerce platform and we work hard each day to make that happen. We are in hyper-growth, and this is where you come in. In your role as a Launch Engineer, you’ll be working with our Shopify Plus merchants on all their big picture technology and systems strategy. You’ll be consulting with merchants on their ecommerce technology stack, as well as providing guidance on how to best leverage the Shopify platform and ecosystem to support their business processes and initiatives. You’ll be directly connected with new Shopify Plus merchants as they come onto our platform. You’ll work with these merchants to ensure that they have a solid plan and timeline for their site launch. Once a shop is comfortably launched, you'll transition them to working directly with their Merchant Success Manager who will help continue to nurture their business from a business growth and strategy perspective. As a subject matter expert on the Shopify Plus platform, you’ll also help to educate and share ecommerce best practices with our merchants.  You’ll also be working closely with our Merchant Success team to consult and provide solutioning support to our Shopify Plus merchants on an ongoing basis. This role is available as a remote position in Ontario, or in-office from Waterloo. The posting will be available until July 25th at 3pm EST, and all candidates will hear back shortly thereafter.
  • Client-side development with JavaScript, HTML and CSS.
  • Experience with Liquid. You won't need to make a theme but you should know how to make small changes and what's possible with our themes.
  • Strong API knowledge.  You won’t need to write code or build an app, but you must be able understand API documentation, use a REST client and know how to conceptualize an API solution.
  • An understanding of commerce best practices, including how to migrate data from other platforms into Shopify.
  • Experience working in an application ecosystem and integrating 3rd party technologies into the Shopify platform.
  • A good project management mindset. This is not a true project management role, but does share some skills with it, especially managing expectations and creating agreement.
  • A deep understanding of technical strategy as it relates to operating and growing a commerce business.
  • A curious mind for how things work and what makes them tick, an affinity for helping and teaching merchants, and a constant thirst to learn about the next best thing.
  • Project management - in some cases you'll be reviewing formal project outlines from merchants to confirm requirements for a successful site launch.
  • Data systems and best practices with interfacing with them.
  • Running your own business.  You know what it means to be an entrepreneur and can share your learnings with our merchants.
  • Building Shopify stores, either for yourself or clients
  • Educating merchants on proper store setup (domains, redirects, product taxonomy, building collections, etc).
  • Working with merchants' internal and 3rd party design and development teams.
  • Consulting with merchants on interesting and complex business system integrations.
  • Helping our merchants to convert their store ideas into real and actionable plans.
  • Providing documentation & support during the store development phase.
  • Liaising with internal Shopify teams, such as the Shopify Plus sales team, the Merchant Success team, Solutions Engineering, and our internal support team.
  • Progressing the site status so stores launch as efficiently as possible.
  • Providing technical support for our Merchant Success team, and in some cases join the call between the MSM and their merchant.
  • Comments
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    Shopify is the longest continuously developed Rails app on the planet. Many core Rails features were actually developed at Shopify, and we’re constantly improving our codebase to make it better or leaner. We’re looking for back-end developers with a passion for solving tough problems with performant code. If you’re interested in helping us build the future of Shopify, this job’s for you. We ship on quality instead of on time. Our teams deploy new code many times a day, and our production scale is massive. We host tens of thousands of online stores, and see hundreds of millions of requests a day. Thousands of merchants will see your work within seconds – a tough but incredibly rewarding responsibility.
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