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Grocery Shopping Application

Flink - Case Study

Flink logo

Go development and QA at a pace that follows business needs

Jan Solecki
Jan Solecki ACCOUNT EXECUTIVE

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The Company

Flink is an online grocery shopping application based in Germany with a bold, consumer-focused mission: to deliver orders within minutes at supermarket prices. It is possible due to the smooth cooperation of multiple applications addressing each step of the delivery process, including mobile apps for the end-users and the e-commerce system, for riders, pickers, and the ERP system.


Flink attracted investors at a record pace and is already available in over 60 cities across four countries. Flink now reaches up to 10 million customers.

flink_project_image
ahmed-khalil
Product and business management from Monterail are amazing. They make sure that we are happy as a client and they are willing to go as far as possible to make sure that the clients’ requirements are met Ahmed Khalil HEAD OF ENGINEERING AT FLINK

Scope and Highlights

  • 10miCustomers
  • 6BACKEND DEVELOPERS
  • 3QA ENGINEERS

The Challenge

Flink (“quick” in German) started as a startup at the end of 2020 and raised $240 million in less than six months. The interest soared during the pandemic, and further funding helped them expand their operations to the Netherlands, France, and Austria.

Their offer is composed of a series of connected apps for different user types, such as customers, riders, and warehouse workers. Flink structures teams narrowly around each app or even specific features. It’s a dynamic setup where staff might be relocated often, to the benefit of efficient implementation.

Early on, they moved the app from React Native to Kotlin & Swift on the frontend but needed assistance making the backend production-ready. Speed was crucial, and outsourcing was the answer, especially considering their accelerated growth.

Flink and Monterail partnered up in March 2021, and initially, Monterail was set to provide Golang and testing expertise.

Key challenges of the project included:

flink mobile mockup
flink mobile app

The Process

Starting from an expert backend code review of Flink apps, we created a list of suggestions and then started implementing them right away. The QAs worked on both backend and frontend, providing everything from ad hoc regression to smoke testing, and ensuring the migration would happen without a hitch.

Beyond migration, Monterail worked on multiple features across the ecosystem. Some highlights include a desktop webshop, checkout and payment functionalities, order location tracking and post-order user experience, user authentication and authorization.

The scope also included systems for back-office operations, covering a warehouse employees app, a dashboard for managing specific orders, and inventory management.

Data migration was an especially interesting challenge. We developed a custom API to transfer data from Saleor to Commerce Tools, affecting several applications in the ecosystem. All under the hood, so end users don’t feel any change.

Along the journey, we helped strategically break down monoliths, such as the checkout and cart systems, into microservices. This separation ensured not only scalability but also work efficiency, as now different developers can contribute more closely with less risk of conflict.

This is how we made it happen:

magdalena-barańska
We joined at an early stage, so it was crucial that our initial code review was done quickly while maintaining high quality. Magdalena Barańska PROJECT MANAGER

The Outcome

Thanks to using the Go language for the project, developers could easily switch teams and work on different applications without a problem. The team, consisting of even up to eleven developers and QA engineers, joined different Flink rockets which enabled fast-paced development and accommodating the dynamic needs of the project.

The partnership gave Flink access to a valuable and flexible pool of first-rate Go developers, QA engineers, and other specialists in a core stage of fast expansion.

With this solid foundation built, our partner is able to more easily include features and scale their efforts across different locations. For example, adding a warehouse to the system began as a complex technical task and now doesn’t require an engineer. It’s easier to add cities and even countries, leaving no roadblocks for accelerated growth.

The success of this project hinged on the following factors: