Deploy .NET 8 Native AOT to AWS Lambda for Ultra‑Fast Serverless Functions

Why native AOT matters for Lambda

Cold‑start latency is the single biggest pain point for high‑traffic serverless workloads. A 2023 benchmark from AWS shows that a typical .NET 6 Lambda starts in 300‑400 ms, while a native AOT binary can be ready in under 50 ms. The reduction comes from eliminating the JIT compiler and trimming unused libraries at build time. For latency‑sensitive APIs, that difference can translate into measurable revenue impact.

Preparing the development environment

Before you write code, verify that your workstation matches the Lambda execution environment. You need .NET SDK 8.0, the Amazon.Lambda.Tools CLI, and Docker (optional but handy for local testing). The following commands install the required tools on a Ubuntu‑based system:

sudo apt-get update && sudo apt-get install -y dotnet-sdk-8.0 unzip zip docker.io
dotnet tool install -g Amazon.Lambda.Tools

Set the PATH so the Lambda tool is available: export PATH=$PATH:~/.dotnet/tools. The same SDK version must be used on the CI pipeline to guarantee reproducible builds.

Creating a .NET 8 AOT project

Start with a minimal Web API template and enable AOT publishing. The PublishAot flag instructs the compiler to emit a native executable for the specified runtime identifier.

<Project Sdk=\"Microsoft.NET.Sdk.Web\">
  <PropertyGroup>
    <TargetFramework>net8.0</TargetFramework>
    <PublishAot>true</PublishAot>
    <RuntimeIdentifier>linux-x64</RuntimeIdentifier>
    <SelfContained>true</SelfContained>
  </PropertyGroup>
</Project>

Add a simple endpoint that returns the current UTC time. The code below lives in Program.cs:

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();
app.MapGet("/time", () => DateTime.UtcNow.ToString("o"));
app.Run();

Because the binary is self‑contained, you do not need the .NET runtime on Lambda – the executable includes everything it needs.

Building the custom runtime bundle

AWS Lambda expects a ZIP file that contains a bootstrap script when you use a custom runtime. The script simply forwards the request to the native binary. Create a file named bootstrap with the following content and give it executable permission:

#!/usr/bin/env bash
set -euo pipefail
exec /var/task/MyAotFunction

Now publish the project and package the binary together with the bootstrap file:

dotnet publish -c Release -r linux-x64 --self-contained true /p:PublishAot=true
cd bin/Release/net8.0/linux-x64/publish
zip -j ../../../../MyAotFunction.zip bootstrap MyAotFunction

The resulting MyAotFunction.zip is ready for upload.

Deploying to AWS Lambda

Use the AWS CLI or the Lambda console to create a function that references the custom runtime. The CLI example below creates the function, sets the handler to bootstrap, and assigns the appropriate execution role:

aws lambda create-function \
  --function-name MyAotFunction \
  --zip-file fileb://MyAotFunction.zip \
  --handler bootstrap \
  --runtime provided.al2 \
  --role arn:aws:iam::123456789012:role/lambda-exec-role \
  --timeout 10 \
  --memory-size 256

After deployment, invoke the function with the test payload from the console or via CLI: aws lambda invoke --function-name MyAotFunction out.txt. The cold‑start time reported by CloudWatch will typically be under 60 ms.

Performance tuning tips

Even with AOT, you can squeeze extra speed by adjusting three settings:

• Memory allocation: Lambda bills per GB‑second, but higher memory also increases CPU share. A 256 MB setting often yields the best latency‑to‑cost ratio for small AOT binaries.
• Trimming: Add <TrimmerRootAssembly>MyAotFunction</TrimmerRootAssembly> to the project file to guarantee unused libraries are removed.
• Environment variables: Set DOTNET_GCServer=1 and DOTNET_TieredCompilation=0 to force server‑GC and disable tiered JIT (the latter is irrelevant for AOT but prevents accidental fallback).

Monitor the Duration metric in CloudWatch after each change; a 5‑10 % improvement is common when fine‑tuning memory.

Conclusion

Deploying a .NET 8 Native AOT application to AWS Lambda eliminates the JIT overhead, shrinks cold‑start latency to sub‑50 ms, and keeps the familiar C# development experience. By following the step‑by‑step workflow—environment setup, project configuration, custom runtime packaging, and Lambda deployment—you can deliver ultra‑fast serverless APIs without abandoning the .NET ecosystem. The performance gains are measurable, the cost impact is modest, and the approach scales from single‑function prototypes to large microservice fleets.

Sources

• Amazon Web Services Documentation – Lambda Custom Runtime
• Microsoft Docs – .NET 8 Native AOT Overview
• AWS Compute Blog – Reducing Lambda Cold Starts with Native Images

Author: Mahmut Sarıkaya — sarikayadev.com