s3-bucket-website-domain-example.yaml

---
AWSTemplateFormatVersion: '2010-09-09'
Resources:
  
  SiteBucket:
    Type: AWS::S3::Bucket
    Properties:
      WebsiteConfiguration:
        ErrorDocument: error.html
        IndexDocument: index.html
  
  SiteBucketPolicy:
    Type: AWS::S3::BucketPolicy
    Properties:
      Bucket:
        Ref: SiteBucket
      PolicyDocument:
        Statement:
          - Action: s3:GetObject
            Effect: Allow
            Principal: '*'
            Resource:
              Fn::Sub: arn:aws:s3:::${SiteBucket}/*
          - Action: s3:ListBucket
            Effect: Allow
            Principal: '*'
            Resource:
              Fn::Sub: arn:aws:s3:::${SiteBucket}
  
  
  
  
  #
  #   S3 Bucket Web Site Domain Formatter Function
  #   
  #   CloudFormation's Fn::GetAtt for an S3Bucket provides two attributes:
  #     * DomainName - DNS Name of the bucket
  #     * WebsiteURL - URL of the website endpoint for the bucket
  #   
  #   However, we want the domain name of the website endpoint for the bucket.
  #   It needs to be specified directly for API Gateway to properly proxy 
  #   requests to it.
  #   
  #   This Lambda function simply strips the domain name from the website URL 
  #   and returns it so it can be exported in the stack's outputs.
  #
  
  S3BucketWebSiteDomainFormatterFunction:
    Type: AWS::Lambda::Function
    Properties:
      Description: Clears out the stack's S3 bucket
      Handler: index.lambda_handler
      MemorySize: 128
      Role:
        Fn::GetAtt:
        - S3BucketWebSiteDomainFormatterFunctionRole
        - Arn
      Code:
        ZipFile: |-
          """S3BucketWebSiteDomainFormatterFunction

          Used as a CloudFormation custom resource to return the domain of a URL.

          """

          from __future__ import print_function

          import json
          import urlparse
          import cfnresponse

          handler_object = None
          def lambda_handler(event, context):
              print("Event: {}".format(json.dumps(event)))
    
              request_type = event.get("RequestType")
    
              response_data = {}
    
              if request_type in ["Create", "Update"]:
                  response_data["WebsiteDomain"] = get_domain_from_url(event["ResourceProperties"]["WebsiteUrl"])
    
              cfnresponse.send(event, context, cfnresponse.SUCCESS, response_data, None)

              return {}

          def get_domain_from_url(website_url):
              parsed_url = urlparse.urlparse(website_url)
              return parsed_url.netloc.split(":")[0]
              
      Runtime: python2.7
      Timeout: '300'

  S3BucketWebSiteDomainFormatterFunctionRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: '2012-10-17'
        Statement:
        - Effect: Allow
          Principal:
            Service:
            - lambda.amazonaws.com
          Action:
          - sts:AssumeRole
      Path: "/"

  S3BucketWebSiteDomainFormatterFunctionRoleActions:
    Type: AWS::IAM::Policy
    Properties:
      PolicyName: S3BucketWebSiteDomainFormatterFunctionRoleActions
      PolicyDocument:
        Version: '2012-10-17'
        Statement:
          - Effect: Allow
            Action:
              - logs:CreateLogStream
              - logs:PutLogEvents
            Resource:
              Fn::Sub: arn:aws:logs:${AWS::Region}:${AWS::AccountId}:log-group:/aws/lambda/${S3BucketWebSiteDomainFormatterFunction}:log-stream:*
      Roles:
        - Ref: S3BucketWebSiteDomainFormatterFunctionRole

  S3BucketWebSiteDomainFormatterFunctionLogGroup:
    Type: AWS::Logs::LogGroup
    Properties:
      LogGroupName:
        Fn::Sub: /aws/lambda/${S3BucketWebSiteDomainFormatterFunction}

  S3BucketWebSiteDomainRetrieval:
    Type: Custom::S3BucketWebSiteDomainRetrieval
    Properties:
      ServiceToken:
        Fn::GetAtt:
        - S3BucketWebSiteDomainFormatterFunction
        - Arn
      WebsiteUrl:
        Fn::GetAtt:
          - SiteBucket
          - WebsiteURL
    DependsOn:
      - S3BucketWebSiteDomainFormatterFunctionLogGroup
      - S3BucketWebSiteDomainFormatterFunctionRoleActions

Outputs:
  S3BucketWebSiteDomain:
    Value:
      Fn::GetAtt:
        - S3BucketWebSiteDomainRetrieval
        - WebsiteDomain