CloudFormation custom resource to create HTTP2 Target Group

cfn-http2-target-group.py

'''
Uses crhelper https://github.com/aws-cloudformation/custom-resource-helper

Requires
- 'elasticloadbalancing:*'
- 'ec2:DescribeInternetGateways'
- 'ec2:DescribeVpcs'
'''

from crhelper import CfnResource
import logging
import boto3
import uuid
from time import sleep

logger = logging.getLogger(__name__)
helper = CfnResource(json_logging=True, log_level='DEBUG',
                     boto_level='CRITICAL')

try:
    elb = boto3.client('elbv2')
except Exception as e:
    helper.init_failure(e)

def without_service_token(event):
    '''Remove ServiceToken from the CloudFormation `event` to so it can be splatted into boto3'''

    return {k: event[k] for k in event if k not in {"ServiceToken"}}


def convertToInt(key, dict):
    if key in dict:
        dict[key] = int(dict[key])


def generateName(prefix):
    return '{}-{}'.format(prefix[0:19], uuid.uuid4().hex.upper()[0:12])


@helper.create
@helper.update
def create(event, context):
    if (event['RequestType'] == 'Update'):
        try:
            logger.info('Replacing target group {}'.format(
                event['PhysicalResourceId']))
            elb.delete_target_group(TargetGroupArn=event['PhysicalResourceId'])
        except Exception as e:
            logging.critical(e, exc_info=True)
            pass

    request = without_service_token(event['ResourceProperties'])

    targetGroupRequest = without_service_token(event['ResourceProperties'])
    del targetGroupRequest['TargetGroupAttributes']

    # fix request payload
    # boto3 expects int but cfn request has converted to str
    convertToInt('HealthCheckIntervalSeconds', targetGroupRequest)
    convertToInt('HealthCheckTimeoutSeconds', targetGroupRequest)
    convertToInt('Port', targetGroupRequest)

    # max 32 characters
    targetGroupRequest['Name'] = generateName(targetGroupRequest['Name'])

    # default to HTTP2, so that it can be overridden to gRPC
    if 'ProtocolVersion' not in targetGroupRequest:
        targetGroupRequest['ProtocolVersion'] = 'HTTP2'

    logger.info('Creating target group')
    logger.info(targetGroupRequest)

    targetGroupResponse = elb.create_target_group(**targetGroupRequest)
    logger.info(targetGroupResponse)
    arn = targetGroupResponse['TargetGroups'][0]['TargetGroupArn']

    attributesRequest = {
        'TargetGroupArn': arn,
        'Attributes': request['TargetGroupAttributes']
    }

    logger.info('Setting target group attributes')
    logger.info(attributesRequest)

    attributesResponse = elb.modify_target_group_attributes(
        **attributesRequest)
    logger.info(attributesResponse)

    return targetGroupResponse['TargetGroups'][0]['TargetGroupArn']


@helper.delete
def delete(event, context):
    try:
        logger.info('Delete target group {}'.format(
            event['PhysicalResourceId']))
        elb.delete_target_group(TargetGroupArn=event['PhysicalResourceId'])
    except Exception as e:
        logging.critical(e, exc_info=True)
        pass

    return


def handler(event, context):
    helper(event, context)

stack.yml

AWSTemplateFormatVersion: 2010-09-09
Description: 'ECS Fargate deployment and dependant resources'

Parameters:
  Name:
    Description: Name
    Type: String
  VpcId:
    Description: VPC Id
    Type: AWS::EC2::VPC::Id
  ServicePort:
    Type: String
    Description: The port of the ECS Service
    
Resources:
  Http2LoadBalancerTargetGroup:
    Type: Custom::Http2TargetGroup
    Properties:
      ServiceToken: !Sub arn:aws:lambda:${AWS::Region}:${AWS::AccountId}:function:cfn-http2-target-group
      Name: !Sub ${Name}-tg
      VpcId: !Ref VpcId
      Protocol: HTTP
      Port: !Ref ServicePort
      TargetType: ip
      TargetGroupAttributes:
        - Key: deregistration_delay.timeout_seconds
          Value: '5'
        - Key: stickiness.enabled
          Value: 'true'
        - Key: stickiness.type
          Value: lb_cookie
        - Key: stickiness.lb_cookie.duration_seconds
          Value: '86400' #1 day
      HealthCheckIntervalSeconds: 300
      HealthCheckTimeoutSeconds: 30
      HealthCheckPath: !Sub /health
      HealthCheckProtocol: HTTP