Category: My Projects
Interview: Inside Shopify’s Modular Monolith
16 Jun2024

This is my interview with Dr. Milan Milanovic originally published on his newsletter Tech World With Milan where we discussed Shopify  architecture, tech stack, testing, culture, and more.

1.  Who is Oleksiy?

I have spent most of my career in technical operations (system administration, later called DevOps, nowadays encompassed by platform engineering and SRE disciplines). Along the way, I worked at Percona as a MySQL performance consultant and then operated some of the largest Ruby on Rails applications in the world, all the while following the incredible story of Shopify’s development and growth.

Finally, after decades of work in operations, when a startup I was at got acquired by Elastic, I decided to move into software engineering. After 5 years there, I needed a bigger challenge, which felt like the right moment to join Shopify.

I started with the Storefronts group (the team responsible for Storefront themes, all the related infrastructure, and the Storefront rendering infrastructure) at Shopify at the beginning of 2022. Two years later, I can confidently say that Shopify’s culture is unique. I enjoy working with the team here due to the incredible talent density I have never encountered. Every day, I am humbled by the caliber of people I can work with and the level of problems I get to solve.

2.  What is the role of the Principal Engineer at Shopify?

Before joining Shopify, I was excited about all the possibilities associated with the Principal Engineer role. Immediately, I was surprised at how diverse the Principal Engineering discipline was at the company. We have a range of engineers here, from extremely deep and narrow experts to amazing architects coordinating challenging projects across the company. Even more impressive is that you have a lot of agency in the shape of a Principal Engineer you will be, provided that the work aligns with the overarching mission of making commerce better for everyone. After 2 years with the company, I found myself in a sweet spot of spending ~75% of my time doing deep technical work across multiple areas of Storefronts infrastructure, and the rest is spent on project leadership, coordination, etc.

3.  The recent tweet by Shopify Engineering shows impressive results achieved by your system. What is Shopify’s overall architecture?

The infrastructure at Shopify was one of the most surprising parts of the company for me. I have spent my whole career building large, heavily loaded systems based on Ruby on Rails. Joining Shopify and knowing upfront a lot about the amount of traffic they handled during Black Friday, Cyber Monday (BFCM), and flash sales, I was half-expecting to find some magic sauce inside. But the reality turned out to be very different: the team here is extremely pragmatic when building anything. It comes from Shopify’s Founder and CEO Tobi Lütke himself: if something can be made simpler, we try to make it so. As a result, the whole system behind those impressive numbers is built on top of fairly common components: Ruby, Rails, MySQL/Vitess, Memcached/Redis, Kafka, Elasticsearch, etc., scaled horizontally.

Shopify Engineering Tweet about the amount of traffic they handled during Black Friday

What makes Shopify unique is the level of mastery the teams have built around those key components: we employ Ruby core contributors (who keep making Ruby faster), Rails core contributors (improving Rails), MySQL experts (who know how to operate MySQL at scale), and we contribute to and maintain all kinds of open-source projects that support our infrastructure. As a result, even the simplest components in our infrastructure tend to be deployed, managed, and scaled exceptionally well, leading to a system that can scale to many orders of magnitude over the baseline capacity and still perform well.

4.  What is Shopify’s tech stack?

Given that databases (and stateful systems in general) are the most complex components to scale, we focus our scaling on MySQL first. All shops on the platform are split into groups, each hosted on a dedicated set of database servers called a pod. Each pod is wholly isolated from the rest of the database infrastructure, limiting the blast radius of most database-related incidents to a relatively small group of shops. Some more prominent merchants get their dedicated pods that guarantee complete resource isolation.

Over the past year, some applications started relying on Vitess to help with the horizontal sharding of their data.

On top of the database layer is a reasonably standard Ruby on Rails stack: Ruby and Rails applications running on Puma, using Memcached for ephemeral storage needs and Elasticsearch for full-text search. Nginx + Lua is used for sophisticated tasks, from smart routing across multiple regions to rate limiting, abuse protection, etc.

This runs on top of Kubernetes hosted on Google Cloud in many regions worldwide, making the infrastructure extremely scalable and responsive to wild traffic fluctuations.

Check the full Shopify tech stack at Stackshare.

A Pods Architecture To Allow Shopify To Scale (Source: Shopify Engineering)

What are Pods exactly?

The idea behind pods at Shopify is to split all of our data into a set of completely independent database (MySQL) clusters using shop_id as the sharding key to ensure resource isolation between different tenants and localize the impact of a “noisy neighbor” problem across the platform. 

Only the databases are podded since they are the hardest component to scale. Everything else that is stateless is scaled automatically according to the incoming traffic levels and other load parameters using a custom Kubernetes autoscale.

5. Is the monolith going to be broken into microservices?

Shopify fully embraces the idea of a Majestic Monolith—most user-facing functionality people tend to associate with the company is served by a single large Ruby on Rails application called “Shopify Core.” Internally, the monolith is split into multiple components focused on different business domains. Many custom (later open-sourced) machinery have been built to enforce coding standards, API boundaries between components, etc.

The rendering application behind all Shopify storefronts is completely separate from the monolith. This was one of the cases where it made perfect sense to split functionality from Core because it is relatively simple. Load data from a database, render Liquid code, and send the HTML back to the user – the absolute majority of requests it handles. Given the amount of traffic on this application, even a small improvement in its efficiency results in enormous resource savings. So, when it was initially built, the team set several strict constraints on how the code is written, what features of Ruby we prefer to avoid, how we deal with memory usage, etc. This allowed us to build a pretty efficient application in a language we love while carefully controlling memory allocation and the resources we spend rendering storefronts.

Shopify application components

In parallel with this effort, the Ruby infrastructure team (working on YJIT, among other things) has made the language significantly faster with each release. Finally, in the last year, we started rewriting parts of this application in Rust to improve efficiency further.

Answering your question about the future of the monolith, I think outside of a few other localized cases, most of the functionality of the Shopify platform will probably be handled by the Core monolith for a long time, given how well it has worked for us so far using relatively standard horizontal scalability techniques.

6. How do you do testing?

Our testing infrastructure is a multi-layered set of checks that allows us to deploy hundreds of times daily while keeping the platform safe. It starts with a set of tests on each application: your typical unit/integration tests, etc. Those are required for a change to propagate into a deployment pipeline (based on the Shipit engine, created by Shopify and open-sourced years ago.

Shopify overall infrastructure

During the deployment, a very important step is canary testing: a change will be deployed onto a small subset of production instances, and automation will monitor a set of key health metrics for the platform. If any metrics move in the wrong direction, the change is automatically reverted and removed from production immediately, allowing developers to figure out what went wrong and try again when they fix the problem. Only after testing a change on canaries for some time the deployment pipeline performs a full deployment. The same approach is used for significant schema changes, etc.

7. How do you do deployments?

All Shopify deployments are based on Kubernetes (running on GCP), so each application is a container (or a fleet of containers) somewhere in one of our clusters. Our deployment pipeline is built on the Shipit engine (created by Shopify and open-sourced years ago). Deployment pipelines can get pretty complex, but it mostly boils down to building an image, deploying it to canaries, waiting to ensure things are healthy, and gradually rolling out the change wider across the global fleet of Kubernetes clusters.

Shipit also maintains the deployment queue and merges multiple pull requests into a single deployment to increase the pipeline’s throughput.

Shipit open-source deployment tool by Shopify (Source)

8. How do you handle failures in the system? 

The whole system is built with many redundancy and horizontal auto-scaling (if possible), which helps prevent large-scale outages. But there are always big and small fires to handle. So, we have a dedicated site reliability team responsible for keeping the platform healthy in the face of constant change and adversarial problems like bots and DDoS attacks. They have built many automated tools to help us handle traffic flashes and, if needed, degrade gracefully. Some interesting examples: they have automated traffic analysis tools helping them scope ongoing incidents down to specific pods, shops, page types, or traffic sources; then the team can control the flow of traffic by pod or shop, re-route traffic between regions, block or slow down requests from specific parts of the world, prioritize particular types of traffic and apply anti-adversarial measures across our network to mitigate attacks.

Finally, each application has an owner team (or a set of teams) that can be paged if their application gets unhealthy. They help troubleshoot and resolve incidents around the clock (being a distributed company helps a lot here since we have people across many time zones).

9. What challenges are you working on right now in your team?

We have just finished a large project to increase the global footprint of our Storefront rendering infrastructure, rolling out new regions in Europe, Asia, Australia, and North America. The project required coordination across many different teams (from networking to databases to operations, etc.) and involved building completely new tools for filtered database replication (since we cannot replicate all of our data into all regions due to cost and data residency requirements), making changes in the application itself to allow for rendering without having access to all data, etc. This large effort has reduced latency for our buyers worldwide and made their shopping experiences smoother.

Next on our radar are further improvements in Liquid rendering performance, database access optimization, and other performance-related work.

Compliance-Driven Development or the Story Behind Swiftype’s SOC2 Certification
18 Jan2018
Based on my experience, just a decade ago not many people within the Silicon Valley startup community considered compliance an important stepping stone in a company’s development roadmap. And when it came to compliance for startups, it was nearly synonymous with PCI/DSS — mandatory certification used by the credit card industry. Over the last few years though, the rise in the number of startups working with large amounts of private and confidential data (fintech, healthcare, etc) and subsequently the rise in the magnitude of data breaches, led our industry to accept the idea that compliance and certifications are not just for the “big guys”. Nowadays, even very small companies are pressed to go through formal certifications if they want people to trust them with private or confidential data.

That is exactly what happened to Swiftype at the beginning of 2017. While preparing for a public release of our latest product (Swiftype Enterprise Search), we understood that it was going to involve a lot of confidential information and we would need to be able to assure our customers of our capabilities to protect their data. In addition to the marketing aspect, there was a security angle to the problem as well: we were looking for a standard framework that could be used by our small team to ensure the safety of customer data, guiding us through the process. Based on those considerations, we decided to go through a formal SOC 2 certification. In this article, I will describe our journey towards the certification and our findings along the way.


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DbCharmer Development: I Give Up
14 Nov2014

About 6 years ago (feels like an eternity in Rails world) working at Scribd I’ve started working on porting our codebase from some old version or Rails to a slightly newer one. That’s when I realized, that there wasn’t a ruby gem to help us manage MySQL connections for our vertically sharded databases (different models on different servers). I’ve started hacking on some code to replace whatever we were using back then, finished the first version of the migration branch and then decided to open the code for other people to use. That’s how the DbCharmer ruby gem was born.

For the next few years a lot of new functionality we needed has been added to the gem, making it more complex and immensely more powerful. I’ve enjoyed working on it, developing those features, contributing to the community. But then I left Scribd, stopped being a user of DbCharmer and the situation drastically changed. For quite some time (years) I would keep fighting to make the code work with newer and newer versions of Rails, struggling to wrap my head around more and more (sometimes useless) abstractions Rails Core team decided to throw into ActiveRecord.

Finally, in the last 2 years (while trying to make DbCharmer compatible with Rails 4.0) it has become more and more apparent, that I simply do not want to do this anymore. I do not need DbCharmer to support Rails 4.0+, while it is very clear that many users need it and constant nagging in the issues and the mailing list, asking for updates generated a lot of anxiety for me, anxiety I couldn’t do much about (the worst kind). As the result, since I simply do not see any good reasons to keep fighting this uphill battle (and developing stuff like this for ActiveRecord IS a constant battle!) I officially give up.

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Interesting Resources for Technical Operations Engineers
23 Sep2013

As a leader of a technical operations team I often have to work on technical operations engineer hiring. This process involves a lot of interviews with candidates and during those interviews along with many challenging practical questions I really love to ask questions like “What are the most important resources you think an Operations Engineer should follow?”, “What books in your opinion are must-read for a techops engineer?” or “Who are your personal heroes in IT community?”. Those questions often give me a lot of information about candidates, their experience, who they are looking up to in the community, what they are interested in, and if they are actively working on improving their professional level.

Recently, one of the candidates asked me to share my lists with him and I thought this information could be valuable to other people so I have decided to share it here on my blog.

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Join Me at Swiftype!
18 Sep2013

As you may have heard, last January I have joined Swiftype – an early stage startup focused on changing local site search for the better. It has been a blast for the past 8 months, we have done a lot of interesting things to make our infrastructure more stable and performant, immensely increased visibility into our performance metrics, developed a strong foundation for the future growth of the company. Now we are looking to expand our team with great developers and technical operations people to push our infrastructure and the product even further.

Since I have joined Swiftype, I have been mainly focused on improving the infrastructure through better automation and monitoring, and worked on our backend code. Now I am looking for a few good operations engineers to join my team to work on a few key projects like building a new multi-datacenter infrastructure, creating a new data storage for our documents data, improving high-availability of our core services and much more.

To help us improve our infrastructure we are looking both for senior operations engineers and for more junior techops people that we could help grow and develop within the company. Both positions could be either remote or we could assist you with relocation to San Francisco if you want to work in our office.

If you are interested, you can take a look at an old, but still pretty relevant post I wrote many years ago on what I believe an ops candidate should know. And, of course, if you have any questions regarding these positions in Swiftype, please email me at [email protected] or use any other means for contacting me and I will try to get back to you as soon as possible. If you know someone who may be a great fit for these positions, please let them know!