サーバレスでPOSTとGETをしてみる

lambdaを使ってPostとgetができるようにする。

my-first-api/                  ← ここがルートフォルダ
├── template.yaml
├── hello_world/
│   └── app.py
├── index.html                 ← ← ← ここに置く！
├── samconfig.toml
└── ...

template.yaml

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31

Resources:
  # ================== API Gateway ==================
  MyApi:
    Type: AWS::Serverless::HttpApi
    Properties:
      StageName: Prod
      CorsConfiguration:
        AllowOrigins:
          - "*"
        AllowMethods:
          - GET
          - POST
          - PUT
          - DELETE
          - OPTIONS
        AllowHeaders:
          - Content-Type
          - Authorization
          - X-Amz-Date
          - X-Api-Key
          - X-Amz-Security-Token
        AllowCredentials: false

  # ================== Lambda関数 ==================
  MyFunction:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: hello_world/
      Handler: app.lambda_handler
      Runtime: python3.12
      Timeout: 10
      MemorySize: 128

      Environment:
        Variables:
          VERSION: "2026.05.10"   # 強制デプロイ用

      Events:
        HelloEvent:
          Type: HttpApi
          Properties:
            ApiId: !Ref MyApi
            Path: /hello
            Method: ANY

        RootEvent:
          Type: HttpApi
          Properties:
            ApiId: !Ref MyApi
            Path: /
            Method: ANY

app.py

import json

def lambda_handler(event, context):
    # CORSヘッダー
    headers = {
        "Content-Type": "application/json",
        "Access-Control-Allow-Origin": "*",
        "Access-Control-Allow-Methods": "GET, POST, OPTIONS",
        "Access-Control-Allow-Headers": "Content-Type, Authorization"
    }

    method = event.get("requestContext", {}).get("http", {}).get("method", "GET")

    if method == "OPTIONS":
        return {"statusCode": 200, "headers": headers, "body": ""}

    if method == "GET":
        body = {"message": "GETでアクセス成功🎉", "method": "GET"}
    
    elif method == "POST":
        try:
            body_data = json.loads(event.get("body", "{}"))
            body = {
                "message": "POSTを受け取りました！",
                "received_data": body_data,
                "method": "POST"
            }
        except:
            body = {"error": "JSONのパースに失敗しました"}
    
    else:
        body = {"error": f"{method} は未対応です"}

    return {
        "statusCode": 200,
        "headers": headers,
        "body": json.dumps(body, ensure_ascii=False)
    }

python3 -m http.server 8000
を実行し

http://localhost:8000/index.html
でgetとpostができることを確認。