Swift is heavily used in production for building cloud services at Apple, with incredible results. Last year, the Password Monitoring service was rewritten in Swift, handling multiple billions of requests per day from devices all over the world. In comparison with the previous Java service, the updated backend delivers a 40% increase in performance, along with improved scalability, security, and availability.

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Apple successfully migrated their Password Monitoring service from Java to Swift, achieving a 40% performance increase while handling billions of daily requests. The migration was driven by Java's garbage collection limitations and scaling challenges. Swift's deterministic memory management reduced memory footprint by an order of magnitude (from gigabytes to hundreds of megabytes), improved bootstrap times for dynamic scaling, and delivered sub-1ms latencies for 99.9% of requests. The rewrite used the Vapor framework and resulted in 85% fewer lines of code while maintaining better safety, readability, and maintainability.

Swift at Apple: migrating the Password Monitoring service from Java

Takeaways for future Swift on server development