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Stripe's meticulous coding process and the Collisons' peculiar peanut analogy🥜

Stripe's codebase consisted of more than 50 million lines of code last year; it's ever-changing and (presumably) ever-growing. Actually implementing those changes, however, is no easy feat. In Stripe's annual letter, founders John and Patrick Collison shed some insight on the lengths the fintech goes to ensure the code its well-paid engineers write fits seamlessly into its broader ecosystem.

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If you want to work as a developer at Stripe, you need to know that here's a lot of code testing. Each change in code is "evaluated by a battery of 1.4 million tests," and its 500k CPUs execute "more than six billion test runs each day." There are many different types of tests implemented, such as end-to-end integrations and cases for specific use cases (such as ensuring that "all code works correctly at unusual times"). Stripe also implements "style checks," presumably to ensure that code is consistent and that a newly arriving engineer won't have to pick up any unintelligible legacy code from a departing engineer. Goldman Sachs uses AI to deal with such problems.

Just in case six billion tests weren't enough, Stripe continues to be cautious when finally implementing code. It's implemented in "pre-production" a mock environment with synthetic data, to see if it can be added (and taken away) without a hitch. Then, it's added to a "single production machine with a small sliver of traffic", then incrementally implemented further until it's a part of all production code. If any "anomalous telemetry" is detected, Stripe automatically redirects traffic to stable legacy systems.

The Collison brothers use a peculiar analogy to explain this thoroughness; it's all in service of preventing a "swollen tongue." Implementing code is like a progressive allergy test: "first rubbing the peanut on your skin, then touching it on the edge of your lip, and then just nibbling the peanut to see if you break out in hives at any point along the way." Right. 🥜

Does this mean developers are waiting around for ages to finally see their changes in action? Perhaps not, as Stripe's aforementioned computing power can do most of this testing very quickly, though Patrick Collison has said employees at Stripe tend to appreciate the "unglamorous" aspects of tech, and may not need instant gratification.

Patrick Collison also recently stressed the importance of being "continually paranoid" of potential pitfalls if you work at Stripe, and this code implementation strategy reflects that. It appears to be successful, too, with Stripe calling itself "best in class" for reliability... but it wants more. The letter states stripe was "only 99.999% available last year," it will presumably be aiming for at least a further decimal place in 2024.

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AUTHORAlex McMurray Editor

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