Amazon VPC サブネットの総/使用済/残 IP アドレス数を CloudWatch に投稿する Lambda Fn

VpcSubnetMetricsCollector.py

import boto3
from datetime import datetime

def lambda_handler(event, context):
    # CloudWatch Metrics に付与するタイムスタンプとして使う
    timestamp = datetime.utcnow()

    client = boto3.client('ec2')
    responses = []
    next_token = None
    while True:
        if next_token is None:
            response = client.describe_subnets()
        else:
            response = client.describe_subnets(NextToken=next_token)
        responses.append(response)
        if not 'NextToken' in response:
            break
        next_token = response['NextToken']

    for response in responses:
        for subnet in response['Subnets']:
            put_subnet_metric(subnet, timestamp)

def put_subnet_metric(subnet, timestamp):
    SubnetMask=int(subnet['CidrBlock'].split('/')[1])
    SubnetTotalIpAddressCount = 2 ** (32 - SubnetMask)
    SubnetUsedIpAddressCount = SubnetTotalIpAddressCount - int(subnet['AvailableIpAddressCount'])

    # 使用可能IPアドレス数
    put_metric_to_cloudwatch(
        'SubnetAvailableIpAddressCount',
        int(subnet['AvailableIpAddressCount']),
        timestamp,
        subnet['VpcId'],
        subnet['SubnetId']
    )

    # 総IPアドレス数
    put_metric_to_cloudwatch(
        'SubnetTotalIpAddressCount',
        SubnetTotalIpAddressCount,
        timestamp,
        subnet['VpcId'],
        subnet['SubnetId']
    )

    # 使用済みIPアドレス数
    put_metric_to_cloudwatch(
        'SubnetUsedIpAddressCount',
        SubnetUsedIpAddressCount,
        timestamp,
        subnet['VpcId'],
        subnet['SubnetId']
    )

def put_metric_to_cloudwatch(metric_name, metric_value, timestamp, vpc_id, subnet_id):
    client = boto3.client('cloudwatch')
    response = client.put_metric_data(
        Namespace='VpcSubnetMetricsCollector',
        MetricData=[
            {
                'MetricName': metric_name,
                'Value': metric_value,
                'Unit': 'Count',
                'Dimensions': [
                  {
                    'Name': 'VpcId',
                    'Value': vpc_id
                  },
                  {
                    'Name': 'SubnetId',
                    'Value': subnet_id
                  }
                ],
                'Timestamp': timestamp
            }
        ]
    )

if __name__ == '__main__':
    lambda_handler('','')