example.py

import boto3

r53_client = boto3.client('route53')

hosted_zone = 'alias.photobox.com.'

def lambda_handler(event = {}, context = {}):
    aws_region = event['detail']['awsRegion']
    elb_client = boto3.client('elb', region_name=aws_region)

    request = event['detail']['requestParameters']
    load_balancer = request['loadBalancerName'] if 'loadBalancerName' in request else request['loadBalancerNames'][0]

    #event sent after a tag addition does not contain the full list of tags,  but just the one created:
    elb_tags = elb_client.describe_tags(LoadBalancerNames=[load_balancer])['TagDescriptions'] or []
    reversed_tags = {x['Value']: x['Key'] for x in elb_tags[0]['Tags'] if elb_tags[0]['Tags'] }
    tags = {v: k for k, v in reversed_tags.items() 

    cluster= tags.get('KubernetesCluster')
    namespace, service_name = tags.get('kubernetes.io/service-name').split('/')
    dns_endpoint = "%s-%s.%s" % (service_name, namespace, args.hosted_zone)
    zone = ( filter(lambda x: x['Name'] == hosted_zone, r53_client.list_hosted_zones()['HostedZones'])[:1] or [None])[0]

    if zone:
        lb = elb_client.describe_load_balancers(LoadBalancerNames=[load_balancer])['LoadBalancerDescriptions'][0]
        lb_zone_id = lb['CanonicalHostedZoneNameID']
        elb_dns_name = lb['DNSName']

        r53_client.change_resource_record_sets(
            HostedZoneId = zone['Id'],
            ChangeBatch={
                'Comment': "Upserting %s for elb %s" % (dns_endpoint, elb_dns_name),
                'Changes':
                [
                    {
                        'Action': 'UPSERT',
                        'ResourceRecordSet': {
                            'Name': dns_endpoint,
                            'Type': 'A',
                            'AliasTarget': {
                                'HostedZoneId': lb['CanonicalHostedZoneNameID'],
                                'DNSName': lb['DNSName'],
                                'EvaluateTargetHealth': True,
                            }
                        }
                    }
                ]
            }
        )