如何通过serverless.yml配置API Gateway REST API无Lambda传文件至S3

是的，你可以不依赖Lambda，直接通过API Gateway的集成请求将文件上传到S3。Serverless Framework本身没有专门的简化配置，但可以通过在serverless.yml中定义自定义CloudFormation资源来实现——因为Serverless的配置本质是基于CloudFormation扩展的。

实现思路 #

API Gateway支持直接与S3集成，通过配置AWS_PROXY类型的集成请求，将上传的文件直接转发到S3存储桶。需要完成以下关键配置：

• 创建API Gateway的REST API资源和方法（比如POST方法）
• 配置该方法的集成请求，目标指向S3存储桶，设置正确的权限和路径映射
• 确保API Gateway有足够的权限向S3写入文件

示例Serverless.yml配置 #

以下是一个完整的示例配置，包含S3存储桶创建、API Gateway集成以及必要的IAM权限：

service: s3-direct-upload-api

provider:
  name: aws
  runtime: python3.9 # 此处指定runtime仅为框架兼容要求，实际不会用到Lambda
  region: us-east-1

resources:
  Resources:
    # 创建S3存储桶
    UploadBucket:
      Type: AWS::S3::Bucket
      Properties:
        BucketName: my-direct-upload-bucket-${self:provider.stage}
        CorsConfiguration:
          CorsRules:
            - AllowedHeaders: ["*"]
              AllowedMethods: ["POST", "PUT"]
              AllowedOrigins: ["*"] # 生产环境请根据实际需求限制来源

    # API Gateway REST API实例
    UploadApi:
      Type: AWS::ApiGateway::RestApi
      Properties:
        Name: S3DirectUploadAPI-${self:provider.stage}

    # API Gateway上传路径资源（/upload）
    UploadResource:
      Type: AWS::ApiGateway::Resource
      Properties:
        ParentId: !GetAtt UploadApi.RootResourceId
        PathPart: upload
        RestApiId: !Ref UploadApi

    # 带文件名参数的子资源（/upload/{filename}）
    UploadFileResource:
      Type: AWS::ApiGateway::Resource
      Properties:
        ParentId: !Ref UploadResource
        PathPart: "{filename}"
        RestApiId: !Ref UploadApi

    # POST方法配置，直接集成S3
    UploadPostMethod:
      Type: AWS::ApiGateway::Method
      Properties:
        AuthorizationType: NONE # 生产环境请配置合适的认证方式（如IAM、Cognito）
        HttpMethod: POST
        Integration:
          Credentials: !GetAtt ApiGatewayS3Role.Arn
          IntegrationHttpMethod: PUT # 映射为S3的PUT上传操作
          Type: AWS_PROXY
          Uri: !Sub "arn:aws:apigateway:${self:provider.region}:s3:path/${UploadBucket}/{filename}"
          RequestParameters:
            integration.request.path.filename: "method.request.path.filename"
            integration.request.header.Content-Type: "method.request.header.Content-Type"
        MethodResponses:
          - StatusCode: 200
        RequestParameters:
          method.request.path.filename: true
          method.request.header.Content-Type: true
        RestApiId: !Ref UploadApi
        ResourceId: !Ref UploadFileResource

    # API Gateway部署
    ApiDeployment:
      Type: AWS::ApiGateway::Deployment
      Properties:
        RestApiId: !Ref UploadApi
        StageName: ${self:provider.stage}
      DependsOn:
        - UploadPostMethod

    # 给API Gateway赋予S3写入权限的IAM角色
    ApiGatewayS3Role:
      Type: AWS::IAM::Role
      Properties:
        AssumeRolePolicyDocument:
          Version: "2012-10-17"
          Statement:
            - Effect: Allow
              Principal:
                Service: apigateway.amazonaws.com
              Action: sts:AssumeRole
        Policies:
          - PolicyName: ApiGatewayS3UploadPolicy
            PolicyDocument:
              Version: "2012-10-17"
              Statement:
                - Effect: Allow
                  Action:
                    - s3:PutObject
                  Resource: !Sub "${UploadBucket.Arn}/*"

  Outputs:
    ApiEndpoint:
      Value: !Sub "https://${UploadApi}.execute-api.${self:provider.region}.amazonaws.com/${self:provider.stage}/upload/{filename}"

关键说明 #

• 通过AWS::ApiGateway::Method配置AWS_PROXY类型集成，将POST请求转换为S3的PUT操作，实现直接上传
• ApiGatewayS3Role专门授权API Gateway向目标S3存储桶执行PutObject操作
• CORS配置用于支持前端直接上传，生产环境需严格限制AllowedOrigins
• 部署完成后，可通过Outputs中的API端点，发送包含文件内容的POST请求到https://<api-id>.execute-api.<region>.amazonaws.com/<stage>/upload/<your-filename>，直接上传文件到S3

为什么Serverless文档里没提到？ #

Serverless Framework的核心设计围绕Lambda函数展开，大部分官方示例和简化配置都是针对Lambda触发的场景。无Lambda的API Gateway集成属于更底层的CloudFormation配置，需要手动定义资源，因此官方文档没有专门章节讲解，但完全支持通过自定义资源实现。

内容的提问来源于stack exchange，提问作者chvc