AWS Lambda API遭CORS策略拦截问题排查求助

我通过Serverless Framework部署了一个Python编写的AWS Lambda API，前端调用时遭遇CORS策略拦截，错误信息如下：

Access to fetch at 'https://0vdu10a3e6.execute-api.eu-west-1.amazonaws.com/dev/init' from origin 'http://localhost:8080' has been blocked by CORS policy: Request header field access-control-allow-origin is not allowed by Access-Control-Allow-Headers in preflight response.

已尝试调整Lambda返回的CORS头配置，但问题仍未解决，且Lambda无日志输出。附上相关配置代码，请求协助排查：

Lambda代码 #

def init(event, context):
       # 省略大部分业务代码
           return {
                "statusCode": 200,
                "headers": {
                    "Access-Control-Allow-Origin": "http://localhost:8080",
                    "Access-Control-Allow-Credentials": True,
                    "Access-Control-Allow-Headers": "Origin, Content-Type, Credentials",
                    "Access-Control-Allow-Methods": "POST, GET",
                    'Content-Type': "application/json"
                },
                "body": json.dumps(response)
            }

Dockerfile #

FROM public.ecr.aws/lambda/python:3.11.2023.09.12.11

WORKDIR /app

COPY Models/best.pt /app
COPY AcharyaMeasuringPrototype.py /app
COPY Utlis.py /app
COPY requirements.txt /app

RUN pip install --upgrade pip

RUN pip cache purge
RUN pip install 'ultralytics[yolo]~=8.0.147'
RUN pip install -r requirements.txt

EXPOSE 3000

CMD [ "AcharyaMeasuringPrototype.init" ]

serverless.yaml #

service: acharya-ml
provider:
  name: aws
  runtime: python3.8
  stage: dev
  region: eu-west-1
  iam:
    role:
      statements:
        - Effect: "Allow"
          Action:
            - "ecr:InitiateLayerUpload"
            - "ecr:SetRepositoryPolicy"
            - "ecr:GetRepositoryPolicy"
          Resource:
            !Join 
              - ':'
              - - 'arn:aws:ecr'
                - Ref: AWS::Region
                - Ref: AWS::AccountId
                - 'repository/*'
plugins:
# - serverless-python-requirements
  - serverless-offline

custom:
  pythonRequirements:
    dockerizePip: true

functions:
  main:
    image: 550512796301.dkr.ecr.eu-west-1.amazonaws.com/acharya-prototype-ml:latest
    timeout: 30
    events:
      - http: 
          path: /init 
          method: POST

前端fetch代码 #

const res = await fetch("https://hinjggqsg4.execute-api.eu-west-1.amazonaws.com/dev/init", {
        method: "POST",
        headers: {
          'Content-Type': 'application/json'
        },
      });

排查方向 #

1. 补全API Gateway CORS配置
   Serverless部署的HTTP API中，OPTIONS预请求默认由API Gateway处理，而非Lambda。需在serverless.yaml的http事件中添加CORS规则，覆盖默认配置：

   events:
     - http: 
         path: /init 
         method: POST
         cors:
           origin: http://localhost:8080
           headers:
             - Content-Type
             - Origin
             - Credentials
           allowCredentials: true
           methods:
             - POST
             - GET
             - OPTIONS
   

2. Lambda显式处理OPTIONS请求
   如果API Gateway未配置自动处理OPTIONS，需在Lambda代码中添加分支逻辑：

   def init(event, context):
       if event['httpMethod'] == 'OPTIONS':
           return {
               "statusCode": 200,
               "headers": {
                   "Access-Control-Allow-Origin": "http://localhost:8080",
                   "Access-Control-Allow-Credentials": True,
                   "Access-Control-Allow-Headers": "Origin, Content-Type, Credentials",
                   "Access-Control-Allow-Methods": "POST, GET, OPTIONS"
               },
               "body": ""
           }
       # 原有业务逻辑代码
   

3. 修复Lambda日志无输出问题
   当前IAM角色缺少CloudWatch日志权限，需补充：

   iam:
     role:
       statements:
         # 保留原有ECR权限
         - Effect: "Allow"
           Action:
             - "logs:CreateLogGroup"
             - "logs:CreateLogStream"
             - "logs:PutLogEvents"
           Resource: "arn:aws:logs:*:*:*"
   

   同时本地运行Docker镜像，验证依赖是否完整、函数能否正常启动。

4. 检查请求头匹配性
   错误提示提到access-control-allow-origin不被允许，确认前端未误发该请求头（当前代码未包含），优先排查前三点配置问题。

内容的提问来源于stack exchange，提问作者Simões