[入門]API Gatewayを利用してS3バケットのオブジェクトを一覧表示させてみた(Lambda統合)

AWSTemplateFormatVersion: "2010-09-09"

Parameters:
  AppName: 
    Description: Application Name.
    Type: String
    Default: api-gateway-s3-list-lambda

Resources:
# ==========
# S3
# ==========
  S3Bucket:
    Type: AWS::S3::Bucket
    Properties:
      BucketEncryption: 
        ServerSideEncryptionConfiguration:
          - ServerSideEncryptionByDefault:
              SSEAlgorithm: AES256
      BucketName: !Sub "api-gateway-s3-${AWS::AccountId}"
      OwnershipControls: 
        Rules:
          - ObjectOwnership: BucketOwnerEnforced
      PublicAccessBlockConfiguration: 
        BlockPublicAcls: true
        BlockPublicPolicy: true
        IgnorePublicAcls: true
        RestrictPublicBuckets: true
# ==========
# Lambda
# ==========
  LambdaExecutionRoleList:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: 2012-10-17
        Statement:
          - Effect: Allow
            Principal:
              Service:
                - lambda.amazonaws.com
            Action:
              - sts:AssumeRole
      ManagedPolicyArns:
        - arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole
      Policies:
        - PolicyName: !Sub ${AppName}-listPolicy
          PolicyDocument:
            Version: 2012-10-17
            Statement:
              - Effect: Allow
                Action:
                  - s3:ListBucket
                Resource: !Sub "arn:aws:s3:::${S3Bucket}"
      Path: /
      RoleName: !Sub ${AppName}-LambdaExecutionRoleList
  LambdaFunctionForList:
    Type: AWS::Lambda::Function
    Properties:
      Code: 
        ZipFile: |
          import boto3
          import json
          import os
          import time

          S3_BUCKET_NAME = os.environ["S3_BUCKET_NAME"]
          s3_client = boto3.client("s3")

          def lambda_handler(event, context):
              params = {'Bucket': S3_BUCKET_NAME}

              objects = []
              response = s3_client.list_objects_v2(**params)

              for obj in response.get('Contents', []):
                  objects.append({
                      'Key': obj['Key'],
                      'Size': obj['Size']
                  })

              body_str = json.dumps(objects)
              return {
                  'statusCode': 200,
                  'body': body_str,
                  'headers': {
                      'Content-Type': "application/json",
                      'Content-Length': str(len(body_str)),
                      'Timestamp': time.strftime("%a, %d %b %Y %H:%M:%S GMT", time.gmtime())
                  }
              }
      Environment: 
        Variables:
          S3_BUCKET_NAME: !Ref S3Bucket
      FunctionName: !Sub ${AppName}-lmd-s3List
      Handler: index.lambda_handler
      MemorySize: 128
      Role: !GetAtt LambdaExecutionRoleList.Arn
      Runtime: python3.12
      Timeout: 10
# ==========
# API Gateway
# ==========
  ApiGatewayRestApi:
    Type: AWS::ApiGateway::RestApi
    Properties:
      BinaryMediaTypes: 
        - 'image/*'
      EndpointConfiguration: 
        Types:
          - REGIONAL
      Name: !Ref AppName
  ApiGatewayMethodRootList:
    Type: AWS::ApiGateway::Method
    Properties:
      AuthorizationType: AWS_IAM
      HttpMethod: GET
      Integration: 
        Type: AWS_PROXY
        IntegrationHttpMethod: POST
        Uri: !Sub 
          - arn:aws:apigateway:${AWS::Region}:lambda:path/2015-03-31/functions/${LambdaArn}/invocations
          - LambdaArn: !GetAtt LambdaFunctionForList.Arn
      MethodResponses: 
        - StatusCode: 200
      ResourceId: !GetAtt ApiGatewayRestApi.RootResourceId
      RestApiId: !Ref ApiGatewayRestApi
  LambdaPermissionRootGET:
    Type: AWS::Lambda::Permission
    Properties:
      Action: lambda:InvokeFunction
      FunctionName: !Ref LambdaFunctionForList
      Principal: apigateway.amazonaws.com
      SourceArn: !Sub 
        - arn:aws:execute-api:${AWS::Region}:${AWS::AccountId}:${MyApi}/*/GET/
        - MyApi: !Ref ApiGatewayRestApi