AWS Lambda Test Tool 0.16.3 incompatible with .NET 8.0 Microsoft.Extensions packages - MissingMethodException

[Jcobb27]

Describe the bug

The AWS .NET 8.0 Mock Lambda Test Tool version 0.16.3 fails to run .NET 8.0 Lambda functions locally that use Host.CreateDefaultBuilder() and Microsoft.Extensions.Hosting 8.0.0. The tool throws MissingMethodException errors for methods that exist in the .NET 8.0 runtime but are missing from the Test Tool's bundled runtime.

The Lambda function was working locally with the Test Tool after upgrading to .NET 8.0 awhile back. The issue appeared recently, suggesting the Test Tool auto-updated to 0.16.3 which introduced this incompatibility.

Regression Issue

• Select this option if this issue appears to be a regression.

Expected Behavior

The AWS .NET 8.0 Mock Lambda Test Tool should successfully run .NET 8.0 Lambda functions that use standard Microsoft.Extensions.Hosting 8.0.0 APIs including:

IHostBuilder.ConfigureServices()
HttpClientFactoryServiceCollectionExtensions.AddHttpClient()
ConsoleLoggerExtensions.AddConsole()

The Lambda should initialize and be testable locally just as it runs in the actual AWS Lambda environment.

Current Behavior

The Test Tool throws MissingMethodException errors during Lambda initialization:

System.MissingMethodException: Method not found: 'Microsoft.Extensions.Hosting.IHostBuilder Microsoft.Extensions.Hosting.IHostBuilder.ConfigureServices(System.Action`1<Microsoft.Extensions.DependencyInjection.IServiceCollection>)'.
at ...Function.constructor()

Additional missing methods:
Method not found: 'Microsoft.Extensions.DependencyInjection.IServiceCollection Microsoft.Extensions.DependencyInjection.HttpClientFactoryServiceCollectionExtensions.AddHttpClient(Microsoft.Extensions.DependencyInjection.IServiceCollection, System.String)'

Method not found: 'Microsoft.Extensions.Logging.ILoggingBuilder Microsoft.Extensions.Logging.ConsoleLoggerExtensions.AddConsole(Microsoft.Extensions.Logging.ILoggingBuilder)'

Reproduction Steps

1. Create a .NET 8.0 Lambda function with the following packages:

Microsoft.Extensions.Hosting 8.0.0
Microsoft.Extensions.Http 8.0.0

2. Use standard Host.CreateDefaultBuilder() pattern in the constructor:

public Function()
{
    var builder = Host.CreateDefaultBuilder();
    builder.ConfigureServices((context, services) =>
    {
        services.AddHttpClient("MyClient");
        services.AddTransient<App>();
    })
    .ConfigureLogging((logging) =>
    {
        logging.AddConsole();
        logging.AddLambdaLogger();
    });

    AppHost = builder.Build();
    ServiceProvider = AppHost.Services;
}

3. Run the Lambda locally using AWS Lambda Test Tool 0.16.3 in Visual Studio
4. Observe MissingMethodException errors

Possible Solution

The Test Tool 0.16.3 appears to bundle an older version of Microsoft.Extensions runtime that doesn't include .NET 8.0 APIs. The tool should either:

1.Include the full .NET 8.0 Microsoft.Extensions runtime, or
2.Use the host machine's installed .NET 8.0 runtime instead of bundling its own

Additional Information/Context

Attempting to manually downgrade to Test Tool 0.15.0 using dotnet tool install -g Amazon.Lambda.TestTool-8.0 --version 0.15.0 gets overridden back to 0.16.3 when running from Visual Studio

Visual Studio shows "AWS .NET 8.0 Mock Lambda Test Tool (0.16.3)" when launching

The issue affects standard Lambda patterns documented in AWS samples

AWS .NET SDK and/or Package version used

Amazon.Lambda.Core 2.2.0
Amazon.Lambda.Serialization.SystemTextJson 2.4.3
Amazon.Lambda.SQSEvents 2.2.0
Microsoft.Extensions.Hosting 8.0.0
Microsoft.Extensions.Http 8.0.0
AWS Lambda Test Tool: 0.16.3

Targeted .NET Platform

.NET 8.0

Operating System and version

Windows 11

[AlexDaines]

Hey @Jcobb27, thanks for the detailed writeup.

This looks related to #2006 - the legacy test tool (the -8.0 version) loads your Lambda's assemblies into its own process, which can cause conflicts with Microsoft.Extensions.* packages. We've seen similar MissingMethodException errors before with this architecture.

That said, your case is a bit different - in #2006 the user was mixing .NET 9 packages with .NET 8, but you're already using 8.0.0 versions which should align. So I want to gather a bit more info:

1. Can you share your full .csproj? Want to check if any transitive deps are pulling in different versions. Running dotnet list package --include-transitive | grep -i microsoft.extensions would help too.

2. Have you tried Lambda Test Tool v2? It runs your Lambda out-of-process and talks to it over HTTP, which avoids the assembly loading issues entirely. It's also closer to how Lambda actually works in AWS.

   • Repo: https://github.com/aws/aws-lambda-dotnet/tree/master/Tools/LambdaTestTool-v2
   • Aspire walkthrough: https://aws.amazon.com/blogs/developer/building-lambda-with-aspire-part-1/

If v2 works for you, that confirms it's the assembly loading issue. If it doesn't, we've got something else going on and will need to dig deeper.

Related: #2006

[Jcobb27]

1. Here's the dependencies in our .csproj. Note that the MPS.* Packages are internally built and include transitive references:

<ItemGroup>
    <PackageReference Include="Amazon.Extensions.Configuration.SystemsManager" Version="6.1.1" />
    <PackageReference Include="Amazon.Lambda.Core" Version="2.2.0" />
    <PackageReference Include="Amazon.Lambda.Logging.AspNetCore" Version="3.1.0" />
    <PackageReference Include="Amazon.Lambda.RuntimeSupport" Version="1.10.0" />
    <PackageReference Include="Amazon.Lambda.Serialization.SystemTextJson" Version="2.4.3" />
    <PackageReference Include="Amazon.Lambda.SQSEvents" Version="2.2.0" />
    <PackageReference Include="AutoMapper" Version="12.0.1" />
    <PackageReference Include="AWSSDK.Extensions.NETCore.Setup" Version="3.7.300" />
    <PackageReference Include="Microsoft.Extensions.Hosting" Version="8.0.0" />
    <PackageReference Include="MPS.Configuration.AWS.Secrets" Version="1.0.14" />
    <PackageReference Include="MPS.Configuration.DI.MS" Version="1.0.58" />
  </ItemGroup>

Here's the output from dotnet list package --include-transitive | Select-String "microsoft.extensions":

   > Microsoft.Extensions.Hosting                        8.0.0       8.0.0
   > Microsoft.Extensions.Caching.Abstractions                                          7.0.0
   > Microsoft.Extensions.Caching.Memory                                                7.0.0
   > Microsoft.Extensions.Configuration                                                 8.0.0
   > Microsoft.Extensions.Configuration.Abstractions                                    8.0.0
   > Microsoft.Extensions.Configuration.Binder                                          8.0.2
   > Microsoft.Extensions.Configuration.CommandLine                                     8.0.0
   > Microsoft.Extensions.Configuration.EnvironmentVariables                            8.0.0
   > Microsoft.Extensions.Configuration.FileExtensions                                  8.0.0
   > Microsoft.Extensions.Configuration.Json                                            8.0.0
   > Microsoft.Extensions.Configuration.UserSecrets                                     8.0.0
   > Microsoft.Extensions.DependencyInjection                                           8.0.1
   > Microsoft.Extensions.DependencyInjection.Abstractions                              8.0.2
   > Microsoft.Extensions.Diagnostics                                                   8.0.0
   > Microsoft.Extensions.Diagnostics.Abstractions                                      8.0.0
   > Microsoft.Extensions.FileProviders.Abstractions                                    8.0.0
   > Microsoft.Extensions.FileProviders.Physical                                        8.0.0
   > Microsoft.Extensions.FileSystemGlobbing                                            8.0.0
   > Microsoft.Extensions.Hosting.Abstractions                                          8.0.0
   > Microsoft.Extensions.Http                                                          8.0.0
   > Microsoft.Extensions.Logging                                                       8.0.1
   > Microsoft.Extensions.Logging.Abstractions                                          8.0.2
   > Microsoft.Extensions.Logging.Configuration                                         8.0.0
   > Microsoft.Extensions.Logging.Console                                               8.0.0
   > Microsoft.Extensions.Logging.Debug                                                 8.0.0
   > Microsoft.Extensions.Logging.EventLog                                              8.0.0
   > Microsoft.Extensions.Logging.EventSource                                           8.0.0
   > Microsoft.Extensions.Options                                                       8.0.2
   > Microsoft.Extensions.Options.ConfigurationExtensions                               8.0.0
   > Microsoft.Extensions.Primitives                                                    8.0.0

2. I wasn't aware of the Lambda Test Tool v2, but I tried it and it works perfectly! It completely bypasses the assembly loading issue. Thanks for the pointer!

[normj]

I'm resolving the ticket since the issue doesn't exist in v2 which will be are main focus going forward. It's design works much better for dependency issues like this then v1. There isn't really a good way to fix the issue in v1. We will aim to make v2 easier to use.

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