CloudFormation API Gateway endpoint calling a Lambda function using proxy integration example.

README.md

CloudFormation API Gateway integration to Lambda function

Template that will create the following:

• API Gateway:
  • Deployed as a REGIONAL endpoint.
  • Single root method, accepting POST requests only, with Lambda proxy integration to a target function.
• In-line Python Lambda function echoing back requesting users IP address to API Gateway requests:
  • IAM role for Lambda allowing CloudWatch logs access.
  • Permissions for Lambda that allow API Gateway endpoint to successfully invoke function.
• CloudWatch logs group for Lambda, with 90 day log retention.

After standing up the template, you will be able to make a HTTP POST request to the URL listed as the apiGatewayInvokeURL output value.

$ curl --request POST https://APIGW_ID.execute-api.AWS_REGION.amazonaws.com/call
# Hello there 127.0.0.1

Reference

• https://docs.aws.amazon.com/apigateway/latest/developerguide/set-up-lambda-proxy-integrations.html#api-gateway-set-up-lambda-proxy-integration-on-proxy-resource.
• https://docs.aws.amazon.com/apigateway/latest/developerguide/api-gateway-create-api-as-simple-proxy-for-lambda.html#api-gateway-proxy-integration-lambda-function-python.
• https://docs.aws.amazon.com/apigateway/api-reference/resource/integration/.
• https://docs.aws.amazon.com/lambda/latest/dg/API_Invoke.html.
• https://docs.aws.amazon.com/lambda/latest/dg/services-apigateway.html#apigateway-permissions.
• https://cjohansen.no/aws-apigw-proxy-cloudformation/.
• https://stackoverflow.com/a/39772260.

stack.yaml

AWSTemplateFormatVersion: 2010-09-09
Description: My API Gateway and Lambda function

Parameters:
  apiGatewayName:
    Type: String
    Default: my-api
  apiGatewayStageName:
    Type: String
    AllowedPattern: "[a-z0-9]+"
    Default: call
  apiGatewayHTTPMethod:
    Type: String
    Default: POST
  lambdaFunctionName:
    Type: String
    AllowedPattern: "[a-zA-Z0-9]+[a-zA-Z0-9-]+[a-zA-Z0-9]+"
    Default: my-function

Resources:
  apiGateway:
    Type: AWS::ApiGateway::RestApi
    Properties:
      Description: Example API Gateway
      EndpointConfiguration:
        Types:
          - REGIONAL
      Name: !Ref apiGatewayName

  apiGatewayRootMethod:
    Type: AWS::ApiGateway::Method
    Properties:
      AuthorizationType: NONE
      HttpMethod: !Ref apiGatewayHTTPMethod
      Integration:
        IntegrationHttpMethod: POST
        Type: AWS_PROXY
        Uri: !Sub
          - arn:aws:apigateway:${AWS::Region}:lambda:path/2015-03-31/functions/${lambdaArn}/invocations
          - lambdaArn: !GetAtt lambdaFunction.Arn
      ResourceId: !GetAtt apiGateway.RootResourceId
      RestApiId: !Ref apiGateway

  apiGatewayDeployment:
    Type: AWS::ApiGateway::Deployment
    DependsOn:
      - apiGatewayRootMethod
    Properties:
      RestApiId: !Ref apiGateway
      StageName: !Ref apiGatewayStageName

  lambdaFunction:
    Type: AWS::Lambda::Function
    Properties:
      Code:
        ZipFile: |
          def handler(event,context):
            return {
              'body': 'Hello there {0}'.format(event['requestContext']['identity']['sourceIp']),
              'headers': {
                'Content-Type': 'text/plain'
              },
              'statusCode': 200
            }
      Description: Example Lambda function
      FunctionName: !Ref lambdaFunctionName
      Handler: index.handler
      MemorySize: 128
      Role: !GetAtt lambdaIAMRole.Arn
      Runtime: python3.8

  lambdaApiGatewayInvoke:
    Type: AWS::Lambda::Permission
    Properties:
      Action: lambda:InvokeFunction
      FunctionName: !GetAtt lambdaFunction.Arn
      Principal: apigateway.amazonaws.com
      # note: if route *not* at API Gateway root, `SourceArn` would take the form of:
      #               arn:aws:execute-api:${AWS::Region}:${AWS::AccountId}:${apiGateway}/${apiGatewayStageName}/${apiGatewayHTTPMethod}/PATH_PART
      SourceArn: !Sub arn:aws:execute-api:${AWS::Region}:${AWS::AccountId}:${apiGateway}/${apiGatewayStageName}/${apiGatewayHTTPMethod}/

  lambdaIAMRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: 2012-10-17
        Statement:
          - Action:
              - sts:AssumeRole
            Effect: Allow
            Principal:
              Service:
                - lambda.amazonaws.com
      Policies:
        - PolicyDocument:
            Version: 2012-10-17
            Statement:
              - Action:
                  - logs:CreateLogGroup
                  - logs:CreateLogStream
                  - logs:PutLogEvents
                Effect: Allow
                Resource:
                  - !Sub arn:aws:logs:${AWS::Region}:${AWS::AccountId}:log-group:/aws/lambda/${lambdaFunctionName}:*
          PolicyName: lambda

  lambdaLogGroup:
    Type: AWS::Logs::LogGroup
    Properties:
      LogGroupName: !Sub /aws/lambda/${lambdaFunctionName}
      RetentionInDays: 90

Outputs:
  apiGatewayInvokeURL:
    Value: !Sub https://${apiGateway}.execute-api.${AWS::Region}.amazonaws.com/${apiGatewayStageName}

  lambdaArn:
    Value: !GetAtt lambdaFunction.Arn