MyProject.csproj

<Project Sdk="Microsoft.NET.Sdk.Web">
  <PropertyGroup>
    <TargetFramework>net6.0</TargetFramework>
    <GenerateRuntimeConfigurationFiles>true</GenerateRuntimeConfigurationFiles>
    <AWSProjectType>Lambda</AWSProjectType>
    
    <!-- This property makes the build directory similar to a publish directory and helps the AWS .NET Lambda Mock Test Tool find project dependencies. -->
    <CopyLocalLockFileAssemblies>true</CopyLocalLockFileAssemblies>
    <PublishReadyToRun>true</PublishReadyToRun>
    <TrimMode>true</TrimMode>
  </PropertyGroup>
  
  <ItemGroup>
    <PackageReference Include="Amazon.Lambda.AspNetCoreServer.Hosting" Version="1.1.0" />
    <PackageReference Include="Amazon.Lambda.Serialization.SystemTextJson" Version="2.2.0" />
    <PackageReference Include="AWSSDK.DynamoDBv2" Version="3.7.0.28" />
  </ItemGroup>
</Project>

Program.cs

using Microsoft.AspNetCore.Builder;
using Microsoft.Extensions.DependencyInjection;
using Amazon.Lambda.Core;
using System;
using Amazon.DynamoDBv2;
using Amazon;
using Amazon.DynamoDBv2.Model;
using System.Collections.Generic;

[assembly: LambdaSerializer(typeof(Amazon.Lambda.Serialization.SystemTextJson.DefaultLambdaJsonSerializer))]

var builder = WebApplication.CreateBuilder(args);

string region = Environment.GetEnvironmentVariable("AWS_REGION") ?? RegionEndpoint.USWest1.SystemName;
string dynamoTable = Environment.GetEnvironmentVariable("SAMPLE_TABLE");

builder.Services.AddSingleton<IAmazonDynamoDB>(new AmazonDynamoDBClient(RegionEndpoint.GetBySystemName(region)) );
builder.Services.AddAWSLambdaHosting(LambdaEventSource.HttpApi);

var app = builder.Build();

app.MapGet("/", () => new List<Guid> {
    Guid.Parse("410a546f-6cb5-4dbd-a334-44507a37a015"),
    Guid.Parse("9f8df297-1998-49f1-823f-de5659d1e3be"),
    Guid.Parse("c30b5b1c-cc27-4d1e-9325-9d6d2e40e931"),
    Guid.Parse("db08fb5d-dead-45eb-9009-b67eafad16a7"),
    Guid.Parse("c2a9f164-3012-4f35-9237-e1602762a8c4")
});
app.MapGet("/{id}", async (IAmazonDynamoDB context, string id) => {
    var results = await context.GetItemAsync(
        new GetItemRequest
        {
            TableName = "helloworldBookCatalog",
            Key = new Dictionary<string, AttributeValue>() {{ "Id", new AttributeValue { S = id }}},
            ProjectionExpression = "Id, ISBN, Title, Authors",
            ConsistentRead = false
        }
    );

    return new {
        Title = results.Item["Title"].S,
        ISBN = results.Item["ISBN"].N,
        Id = results.Item["Id"].S,
    };
});
app.Run();