AWSTemplateFormatVersion: 2010-09-09
Description: A public ALB with a Lambda Function target.
Transform: AWS::Serverless-2016-10-31

Parameters:

  DeploymentName:
    Type: String
    Description: A name for this deployment

Resources:

  ALB:
    Type: AWS::ElasticLoadBalancingV2::LoadBalancer
    Properties:
      IpAddressType: ipv4
      Scheme: internet-facing
      SecurityGroups: [!Ref AlbSecurityGroup]
      Subnets:
        - Fn::ImportValue: !Sub "${DeploymentName}-PublicSubnet1"
        - Fn::ImportValue: !Sub "${DeploymentName}-PublicSubnet2"
      Type: application
      Tags:
        - Key: Name
          Value: !Ref AWS::StackName

  AlbSecurityGroup:
    Type: AWS::EC2::SecurityGroup
    Properties:
      GroupDescription: Allow HTTP on port 80
      VpcId: {Fn::ImportValue: !Sub "${DeploymentName}-VpcId"}
      SecurityGroupIngress:
        - IpProtocol: tcp
          FromPort: 80
          ToPort: 80
          CidrIp: 0.0.0.0/0
      Tags:
        - Key: Name
          Value: !Ref AWS::StackName

  ALBListenerHTTP:
    Type: AWS::ElasticLoadBalancingV2::Listener
    Properties:
      DefaultActions:
        - Type: forward
          TargetGroupArn: !Ref AlbTargetGroupLambda
      LoadBalancerArn: !Ref ALB
      Port: 80
      Protocol: HTTP

  AlbTargetGroupLambda:
    Type: AWS::ElasticLoadBalancingV2::TargetGroup
    DependsOn: LambdaInvokePermissionElb
    Properties:
      TargetType: lambda
      Targets:
        - Id: !GetAtt HelloWorldFunction.Arn

  LambdaInvokePermissionElb:
    Type: AWS::Lambda::Permission
    DependsOn: HelloWorldFunction
    Properties:
      FunctionName: !Ref HelloWorldFunction
      Action: lambda:InvokeFunction
      Principal: elasticloadbalancing.amazonaws.com

  HelloWorldFunction:
    Type: AWS::Serverless::Function
    Properties:
      FunctionName: !Sub "${DeploymentName}-Hello-World"
      InlineCode: |
        import json
        def handler(event, context) -> dict:
            message = {"hello": "world"}
            response = {
                "statusCode": 200,
                "statusDescription": "200 OK",
                "headers": {"Content-Type": "application/json"},
                "body": json.dumps(message),
            }
            return response
      Handler: index.handler
      Runtime: python3.8
      Timeout: 3

Outputs:
  ALB:
    Description: DNS name for the ALB
    Value: !GetAtt ALB.DNSName
    Export:
      Name: !Sub "${DeploymentName}-ALB"