How Swift on Kubernetes Boosted Performance 4× and Cut Costs by 66%

Swift is primarily used for app development on Apple computers and devices, but it can also be employed on the server side.

Although server‑side Swift has lagged behind, with early support from IBM’s Kitura framework discontinued in 2019, the idea of using a single language for both client and server remains attractive.

Cultured Code, the maker of the popular task‑manager app for Apple platforms, replaced its Python 2 application running on Google App Engine with a Swift service deployed on a Kubernetes cluster in AWS.

According to Vojtěch Rylko (developer) and CEO Werner Jainek, the migration quadrupled the average response time of the cloud‑based app that synchronises data across devices and cut the average compute cost to one‑third.

They noted that the legacy Python code suffered from lack of static typing, risky changes, slow response, and high memory usage, making a full rewrite the only viable solution.

The new Swift application consists of roughly 30,000 lines of code, built with Xcode in about ten minutes, and runs on a small four‑node Kubernetes cluster using AWS Aurora MySQL and Redis for temporary data storage.

Python is still used for a small AWS Lambda service that handles email processing, due to the absence of mature Swift libraries for that purpose.

The team encourages other developers to explore server‑side Swift, citing recent work on Swift‑Java interoperability that could ease gradual adoption, and emphasizing the simplification of programming from device to cloud when staying within the Apple ecosystem.

However, they also acknowledge risks such as less mature server‑side support for Swift and longer build times that can frustrate developers.