template.yaml

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description:  API Gateway REST API with Lambda Proxy integration and CORS enabled (uksb-1tthgi812) (tag:apigw-cors-proxy)

Resources:
    ApiGatewayRestApi:
      Type: AWS::ApiGateway::RestApi
      Properties:
        Description: API with Cors Support
        EndpointConfiguration:
          Types:
            - REGIONAL
        Name: cors-api

    ApiGatewayResource:
      Type: AWS::ApiGateway::Resource
      Properties:
        ParentId: !GetAtt ApiGatewayRestApi.RootResourceId
        PathPart: 'helloworld'
        RestApiId: !Ref ApiGatewayRestApi
    
    ApiGatewayGetMethod:
      Type: AWS::ApiGateway::Method
      Properties:
        AuthorizationType: NONE
        HttpMethod: GET
        Integration:
          IntegrationHttpMethod: POST
          IntegrationResponses:
           -
            ResponseParameters:
               method.response.header.Access-Control-Allow-Headers: "'Content-Type,X-Amz-Date,Authorization,X-Api-Key,X-Amz-Security-Token'"
               method.response.header.Access-Control-Allow-Methods: "'POST,GET,OPTIONS'"
               method.response.header.Access-Control-Allow-Origin: "'*'"
            StatusCode: '200'
          Type: AWS
          Uri: !Sub "arn:aws:apigateway:${AWS::Region}:lambda:path/2015-03-31/functions/${MyFunction.Arn}/invocations"
        MethodResponses:
         -
           ResponseParameters:
             method.response.header.Access-Control-Allow-Headers: true
             method.response.header.Access-Control-Allow-Methods: true
             method.response.header.Access-Control-Allow-Origin: true
           StatusCode: '200'
        OperationName: 'helloworld'
        ResourceId: !Ref ApiGatewayResource
        RestApiId: !Ref ApiGatewayRestApi

    ApiGatewayOptionsMethod:
      Type: AWS::ApiGateway::Method
      Properties:
        AuthorizationType: NONE
        HttpMethod: OPTIONS
        Integration:
          IntegrationHttpMethod: POST
          Type: AWS_PROXY
          Uri: !Sub "arn:aws:apigateway:${AWS::Region}:lambda:path/2015-03-31/functions/${MyFunctionOptions.Arn}/invocations"
        OperationName: 'helloworld'
        ResourceId: !Ref ApiGatewayResource
        RestApiId: !Ref ApiGatewayRestApi

    MyFunction:
        Type: AWS::Serverless::Function
        Properties:
            Handler: index.handler
            Runtime: python3.7
            InlineCode: | 
                import json 
                def handler(event, context): 
                    return { 
                "statusCode": 200, 
                "body": json.dumps({ "message" : "Hello from Lambda!"}), 
                }

    MyFunctionPermission:
        Type: AWS::Lambda::Permission
        DependsOn:
        - ApiGatewayRestApi
        Properties:
          Action: lambda:InvokeFunction
          FunctionName: !Ref MyFunction
          Principal: apigateway.amazonaws.com
    
    MyFunctionOptions:
        Type: AWS::Serverless::Function
        DependsOn: ApiGatewayRestApi
        Properties:
            Handler: index.handler
            Runtime: python3.7
            InlineCode: | 
                import json 
                def handler(event, context): 
                    return { 
                        "statusCode": 200, 
                        "headers": {
                            "Access-Control-Allow-Origin": '*',
                            "Access-Control-Allow-Headers": 'Content-Type,Authorization,X-AMZ-Date,X-Api-Key,X-AMZ-Security-Token',
                            "Access-Control-Allow-Methods": 'GET,POST,OPTIONS'
                            }
                }

    MyFunctionOptionsPermission:
        Type: AWS::Lambda::Permission
        DependsOn:
        - ApiGatewayRestApi
        Properties:
          Action: lambda:InvokeFunction
          FunctionName: !Ref MyFunctionOptions
          Principal: apigateway.amazonaws.com

    Deployment:
      Type: AWS::ApiGateway::Deployment
      DependsOn: ApiGatewayGetMethod
      Properties:
        RestApiId: !Ref ApiGatewayRestApi
        StageName: prod