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== Cold Start Performance and Deployment Considerations ==
Rust and Go generally exhibit lower cold start times in AWS Lambda compared to Java and C# <ref>{{Cite web |date=2023-04-13 |title=Optimizing AWS Lambda extensions in C# and Rust {{!}} AWS Compute Blog |url=https://aws.amazon.com/blogs/compute/optimizing-aws-lambda-extensions-in-c-and-rust/ |access-date=2025-03-20 |website=aws.amazon.com |language=en-US}}</ref>because they compile to native static binaries, eliminating the need for a virtual machine (JVM or .NET CLR) and reducing runtime initialization overhead. Go has some minimal runtime initialization, including garbage collection and goroutine management, but its impact on cold start time is relatively low. Rust, which is fully ahead-of-time (AOT) compiled and does not require a runtime, often achieves the lowest cold start latency among supported languages. <ref name=":9">{{Cite book |last=Chapin |first=John |title=Programming AWS Lambda: build and deploy serverless applications with Java |last2=Roberts |first2=Mike |date=2020 |publisher=O'Reilly |isbn=978-1-4920-4102-3 |___location=Beijing Boston Farnham Sebastopol Tokyo}}</ref><ref name=":6" /><ref>{{Cite web |date=2021-04-26 |title=Operating Lambda: Performance optimization – Part 1 {{!}} AWS Compute Blog |url=https://aws.amazon.com/blogs/compute/operating-lambda-performance-optimization-part-1/ |access-date=2025-03-20 |website=aws.amazon.com |language=en-US}}</ref><ref>{{Cite web |title=Understanding the Lambda execution environment lifecycle - AWS Lambda |url=https://docs.aws.amazon.com/lambda/latest/dg/lambda-runtime-environment.html |access-date=2025-03-20 |website=docs.aws.amazon.com}}</ref><ref>{{Cite web |title=Define Lambda function handler in Rust - AWS Lambda |url=https://docs.aws.amazon.com/lambda/latest/dg/rust-handler.html#rust-best-practices |access-date=2025-03-20 |website=docs.aws.amazon.com}}</ref><ref>{{Cite web |title=Define Lambda function handlers in Go - AWS Lambda |url=https://docs.aws.amazon.com/lambda/latest/dg/golang-handler.html#go-best-practices |access-date=2025-03-20 |website=docs.aws.amazon.com}}</ref>
Java and C# run on managed runtime environments, introducing additional cold start latency due to runtime initialization and Just-In-Time (JIT) compilation. However, modern optimizations have mitigated some of these challenges. .NET 7 and .NET 8 support Ahead-of-Time (AOT) compilation, reducing cold start times by precompiling code. <ref>{{Cite web |title=Building .NET Lambda functions with Native AOT compilation in AWS SAM - AWS Serverless Application Model |url=https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/build-dotnet7.html |access-date=2025-03-20 |website=docs.aws.amazon.com}}</ref><ref>{{Cite web |date=2024-02-22 |title=Introducing the .NET 8 runtime for AWS Lambda {{!}} AWS Compute Blog |url=https://aws.amazon.com/blogs/compute/introducing-the-net-8-runtime-for-aws-lambda/ |access-date=2025-03-20 |website=aws.amazon.com |language=en-US}}</ref> Additionally, AWS Lambda SnapStart for Java 11 and 17 pre-warms and snapshots execution state, significantly decreasing cold start overhead for Java-based functions. <ref>{{Cite web |date=2022-11-29 |title=Reducing Java cold starts on AWS Lambda functions with SnapStart {{!}} AWS Compute Blog |url=https://aws.amazon.com/blogs/compute/reducing-java-cold-starts-on-aws-lambda-functions-with-snapstart/ |access-date=2025-03-20 |website=aws.amazon.com |language=en-US}}</ref><ref>{{Cite web |title=Improving startup performance with Lambda SnapStart - AWS Lambda |url=https://docs.aws.amazon.com/lambda/latest/dg/snapstart.html |access-date=2025-03-20 |website=docs.aws.amazon.com}}</ref> Despite these optimizations, Rust and Go typically maintain lower cold start times due to their minimal runtime dependencies. <ref name=":9" /><ref name=":6" />
In long-running workloads, JIT compilation in Java and .NET may improve execution speed through dynamic optimizations. However, this benefit is workload-dependent, and Rust’s AOT compilation often provides better performance consistency, particularly for CPU-bound tasks. <ref>{{Cite web |title=Compile .NET Lambda function code to a native runtime format - AWS Lambda |url=https://docs.aws.amazon.com/lambda/latest/dg/dotnet-native-aot.html |access-date=2025-03-20 |website=docs.aws.amazon.com}}</ref> For short-lived Lambda invocations, Rust and Go generally maintain more predictable performance, as JIT optimizations may not have sufficient time to take effect. <ref name=":6" /><ref>{{Cite web |title=Customize Java runtime startup behavior for Lambda functions - AWS Lambda |url=https://docs.aws.amazon.com/lambda/latest/dg/java-customization.html |access-date=2025-03-20 |website=docs.aws.amazon.com}}</ref>
Historically, Rust and Go required additional effort in deployment due to cross-compilation and static linking challenges. Rust, in particular, often necessitates MUSL-based static linking for AWS Lambda compatibility. However, advancements in deployment tooling, including AWS Serverless Application Model (AWS SAM), GitHub Actions, and Lambda container images, have simplified this process. Go benefits from native static linking support, making its deployment process comparatively straightforward. AWS Lambda's support for container images further reduces runtime compatibility concerns, enabling the use of custom runtimes and dependencies. <ref name=":9" /><ref name=":6" /><ref>{{Cite web |title=Building Lambda functions with Rust - AWS Lambda |url=https://docs.aws.amazon.com/lambda/latest/dg/lambda-rust.html |access-date=2025-03-20 |website=docs.aws.amazon.com}}</ref><ref>{{Cite web |title=Building Rust Lambda functions with Cargo Lambda in AWS SAM - AWS Serverless Application Model |url=https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/building-rust.html |access-date=2025-03-20 |website=docs.aws.amazon.com}}</ref><ref>{{Cite web |title=Generate a starter CI/CD pipeline with AWS SAM - AWS Serverless Application Model |url=https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/serverless-generating-example-ci-cd.html |access-date=2025-03-20 |website=docs.aws.amazon.com}}</ref><ref>{{Cite web |date=2022-01-24 |title=Migrating AWS Lambda functions to Arm-based AWS Graviton2 processors {{!}} AWS Compute Blog |url=https://aws.amazon.com/blogs/compute/migrating-aws-lambda-functions-to-arm-based-aws-graviton2-processors/ |access-date=2025-03-20 |website=aws.amazon.com |language=en-US}}</ref>
==Features==
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