.NET 6 Web API部署Lambda后无法处理SQS队列请求

问题场景 #

• 基于.NET 6 Core Web API构建项目，通过builder.Services.AddAWSLambdaHosting(LambdaEventSource.HttpApi);转为Lambda并通过CLI部署
• POSTMAN调用Lambda函数正常，但通过AWS控制台的SQS队列发送消息触发时，抛出空引用异常

异常日志 #

2023-02-01T00:38:06.905Z    04b8dce2-d17c-5125-88d3-80b167d862bd    fail    System.NullReferenceException: Object reference not set to an instance of an object.
   at Amazon.Lambda.AspNetCoreServer.APIGatewayHttpApiV2ProxyFunction.MarshallRequest(InvokeFeatures features, APIGatewayHttpApiV2ProxyRequest apiGatewayRequest, ILambdaContext lambdaContext)
   at Amazon.Lambda.AspNetCoreServer.AbstractAspNetCoreFunction`2.FunctionHandlerAsync(TREQUEST request, ILambdaContext lambdaContext)
   at Amazon.Lambda.RuntimeSupport.HandlerWrapper.<>c__DisplayClass26_0`2.<GetHandlerWrapper>b__0.MoveNext()
--- End of stack trace from previous location ---
   at Amazon.Lambda.RuntimeSupport.LambdaBootstrap.InvokeOnceAsync(CancellationToken cancellationToken)

测试消息 #

POSTMAN/SQS直接发送的消息 #

{
    "nameOnCard": "Samuel Ojo",
    "cardNumber": "5256854950074930",
    "cvv": "283",
    "expiryMonth": "04",
    "expiryYear": "27",
    "postalCode": "101232",
    "billingAddress": "Lagos",
    "billingState": "Lagos",
    "billingCity": "Lagos",
    "billingCountry": "Nigeria",
    "awsSettings": {
        "topicArn": [redacted],
        "targetArn": [redacted],
        "snsTopicFilter": "VirtualCard"
    }
}

SQS模板消息 #

{
  "Records": [
    {
      "messageId": "19dd0b57-b21e-4ac1-bd88-01bbb068cb78",
      "receiptHandle": "MessageReceiptHandle",
      "body": "{\"sourceAccount\": \"0123445599\",\"destinationAccount\": \"1838494040\",\"bankCode\": \"011\",\"amount\": 200,\"awsSettings\": {\"topicArn\": [redacted],\"targetArn\": [redacted],\"snsTopicFilter\": \"FundTransfer\"}}",
      "attributes": {
        "ApproximateReceiveCount": "1",
        "SentTimestamp": "1523232000000",
        "SenderId": "123456789012",
        "ApproximateFirstReceiveTimestamp": "1523232000001"
      },
      "messageAttributes": {},
      "md5OfBody": "{{{md5_of_body}}}",
      "eventSource": "aws:sqs",
      "eventSourceARN": "arn:aws:sqs:us-east-1:123456789012:MyQueue",
      "awsRegion": "us-east-1"
    }
  ]
}

Program.cs代码 #

using VirtualCardService.Middlewares;
using VirtualCardService.Services.Contracts;

var builder = WebApplication.CreateBuilder(args);

#region Add Services to Container

builder.Services.AddControllers();
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();
builder.Services.AddScoped<IVirtualCardService, VirtualCardService.Services.Implementations.VirtualCardService>();
builder.Services.AddAWSLambdaHosting(LambdaEventSource.HttpApi);
#endregion

var app = builder.Build();

#region Configure Pipeline

if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}

app.UseHttpsRedirection();

app.Use((context, next) =>
{
    context.Request.EnableBuffering();
    return next();
});

app.UseRouting();
app.UseMiddleware<HttpLoggerMiddleware>();
app.UseMiddleware<ExceptionMiddleware>();

app.UseAuthorization();
app.MapControllers();
#endregion

app.Run();

问题原因及解决方法 #

原因 #

当前Lambda通过LambdaEventSource.HttpApi配置为仅支持HttpApi触发，而SQS触发的事件格式与HttpApi请求结构完全不兼容。APIGatewayHttpApiV2ProxyFunction尝试将SQS事件转换为ASP.NET Core请求时，找不到预期的HttpApi请求字段，从而抛出空引用异常。

解决步骤 #

1. 修改Lambda处理逻辑，支持多事件源
   不能仅依赖AddAWSLambdaHosting的HttpApi模式，需要自定义Lambda入口函数，分别处理HttpApi请求和SQS事件：

   • 创建自定义Lambda入口类，继承APIGatewayHttpApiV2ProxyFunction处理Http请求，同时添加SQS事件处理方法。

2. 示例修改方案
   移除Program.cs中的builder.Services.AddAWSLambdaHosting(LambdaEventSource.HttpApi);，新增Lambda入口类：

   // LambdaEntryPoint.cs
   using Amazon.Lambda.AspNetCoreServer;
   using Amazon.Lambda.SQSEvents;
   using Microsoft.AspNetCore.Hosting;
   using VirtualCardService.Services.Contracts;
   
   namespace VirtualCardService;
   
   public class LambdaEntryPoint : APIGatewayHttpApiV2ProxyFunction
   {
       protected override void Init(IWebHostBuilder builder)
       {
           builder.ConfigureServices(services =>
           {
               // 注册原有服务
               services.AddControllers();
               services.AddScoped<IVirtualCardService, Services.Implementations.VirtualCardService>();
           }).Configure(app =>
           {
               // 配置原有管道逻辑
               if (app.Environment.IsDevelopment())
               {
                   app.UseSwagger();
                   app.UseSwaggerUI();
               }
               app.UseHttpsRedirection();
               app.UseRouting();
               app.UseMiddleware<HttpLoggerMiddleware>();
               app.UseMiddleware<ExceptionMiddleware>();
               app.UseAuthorization();
               app.MapControllers();
           });
       }
   
       // 处理SQS事件的方法
       public async Task HandleSQSAsync(SQSEvent sqsEvent, ILambdaContext context)
       {
           using var scope = ServiceProvider.CreateScope();
           var cardService = scope.ServiceProvider.GetRequiredService<IVirtualCardService>();
   
           foreach (var record in sqsEvent.Records)
           {
               // 解析消息体并调用业务逻辑
               context.Logger.LogInformation($"Processing SQS message: {record.Body}");
               // 替换为你的业务处理代码
               // await cardService.YourBusinessMethod(record.Body);
           }
       }
   }
   

   部署时指定Lambda处理器：

   • HttpApi触发：VirtualCardService::VirtualCardService.LambdaEntryPoint::FunctionHandlerAsync
   • SQS触发：VirtualCardService::VirtualCardService.LambdaEntryPoint::HandleSQSAsync

3. 简化替代方案
   如果业务允许，可拆分两个Lambda函数：一个专门处理HttpApi请求，另一个处理SQS事件，共享业务逻辑层代码，避免混合处理的复杂度。

内容的提问来源于stack exchange，提问作者Samuel Babbs