The Datadog team reengineered their AWS Lambda extension to deliver high-fidelity telemetry with minimal overhead, resulting in a 82% reduction in cold start latency and a 40% reduction in memory usage. The rewrite was done using Rust, which provided significant benefits including tiny binaries, excellent concurrency primitives, and memory safety enforced at compile time. The team carefully balanced design constraints such as minimizing impact on the running Lambda function handler code and reducing CPU consumption during the invoke phase. They also implemented a failover strategy to deliver performance improvements to customers while having a gradual migration process. The project demonstrates the potential of Rust for Lambda extensions, with reduced binary size from 55 MB to just 7 MB, and extremely fast cold start times of around 70 ms.