.NET Core 6+AWS Lambda无法处理请求体中的Base64数据

使用VS 2022的「发布到Lambda」工具将.NET Core极简API部署至AWS Lambda，API功能为接收图片Base64字符串并上传至S3。调用接口时，若传入photo参数（非空Base64字符串），Lambda返回**(504)网关超时**；但photo为空时，端点可正常响应。

相关配置 #

1. Program.cs 托管代码 #

builder.Services.AddAWSLambdaHosting(LambdaEventSource.RestApi);

2. Postman 请求体 #

{
    "photo": "/9j/4AAQSkZ.....",
    "ext": "png"
}

3. server.template 配置 #

{
  "AWSTemplateFormatVersion": "2010-09-09",
  "Transform": "AWS::Serverless-2016-10-31",
  "Description": "An AWS Serverless Application that uses the ASP.NET Core framework running in Amazon Lambda.",
  "Parameters": {},
  "Conditions": {},
  "Resources": {
    "AspNetCoreFunction": {
      "Type": "AWS::Serverless::Function",
      "Properties": {
        "Handler": "xxx",
        "Runtime": "dotnet6",
        "CodeUri": "",
        "MemorySize": 256,
        "Timeout": 30,
        "Role": null,
        "Policies": [
          "AWSLambda_FullAccess",
          "AWSLambdaVPCAccessExecutionRole"
        ],
        "Events": {
          "ProxyResource": {
            "Type": "Api",
            "Properties": {
              "Path": "/{proxy+}",
              "Method": "ANY"
            }
          },
          "RootResource": {
            "Type": "Api",
            "Properties": {
              "Path": "/",
              "Method": "ANY"
            }
          }
        }
      }
    }
  },
  "Outputs": {
    "ApiURL": {
      "Description": "API endpoint URL for Prod environment",
      "Value": {
        "Fn::Sub": "https://${ServerlessRestApi}.execute-api.${AWS::Region}.amazonaws.com/Prod/"
      }
    }
  }
}

4. aws-lambda-tools-defaults.json 配置 #

{
    "Information" : [
        "...."
    ],
    "profile"     : "default",
    "region"      : "ap-southeast-1",
    "configuration" : "Release",
    "s3-prefix"     : "xxx/",
    "template"      : "serverless.template",
    "template-parameters" : "",
    "s3-bucket"           : "xxx",
    "stack-name"          : "xxx"
}

排查与解决方法 #

• 调整超时配置：API Gateway默认同步超时为29秒，当前LambdaTimeout设为30秒，会导致网关先触发超时。将Lambda的Timeout改为28秒以内；若需处理大文件，启用API Gateway异步调用模式。
• 提升Lambda资源配置：Base64解码和S3上传对内存、CPU需求较高，当前256MB内存可能导致性能瓶颈。将MemorySize提升至512MB或更高，Lambda的CPU性能随内存线性增长，能有效缩短执行时间。
• 检查VPC网络连通性：模板包含AWSLambdaVPCAccessExecutionRole权限，若Lambda关联了VPC但未配置S3网关端点或NAT网关，会无法访问S3导致请求挂起。若不需要VPC，移除该权限并取消VPC配置；若必须用VPC，添加对应网络组件确保S3访问正常。
• 查看CloudWatch日志定位异常：登录AWS控制台进入CloudWatch日志组，查看Lambda执行日志，确认是Base64解码失败、S3上传超时还是其他错误导致执行停滞，针对性修复代码逻辑。

内容的提问来源于stack exchange，提问作者M. Ko