From https://aws.amazon.com/blogs/aws/amazon-ebs-update-new-elastic-volumes-change-everything/

lambda-resize-ebs

from __future__ import print_function
import boto3
ec2 = boto3.client('ec2')
ssm = boto3.client('ssm')
tags ={'Key': os.environ['Tagname'], 'Value': os.environ['Tagvalue']}

def find_viable_window ():
    #checks if the Tag Key value pair matches with an existing Maintenance Window
    wins = ssm.describe_maintenance_windows()['WindowIdentities']
    for win in wins:
        tgts = ssm.describe_maintenance_window_targets(WindowId=win['WindowId'])['Targets']
        for tgt in tgts:
            t = tgt['Targets'][0]['Key'].split(':')
            v = tgt['Targets'][0]['Values'][0]
            if len(t) > 1 and t[0] == 'tag' and t[1] == tags['Key'] and v == tags['Value']:
                return True;
    return False;

def lambda_handler(event, context):
    volume =(event['resources'][0].split('/')[1])
    if event['detail']['result'] == 'completed':
        attach=ec2.describe_volumes(VolumeIds=[volume])['Volumes'][0]['Attachments']
        if attach: 
            instance = attach[0]['InstanceId']
            filter={'key': 'InstanceIds', 'valueSet': [instance]}
            info = ssm.describe_instance_information(InstanceInformationFilterList=[filter])['InstanceInformationList']
            if info:
                ec2.create_tags(Resources=[instance],Tags=[tags])
                if not find_viable_window():
                    print "WARNING: the proposed tags {0} : {1} are not a valid target in any maintenance window \n The changes will not be automatically applied".format(tags['Key'],tags['Value'])
                print "{0} Instance {1} has been tagged for maintenance".format(info[0]['PlatformName'], instance)
            else:
                raise Exception('Instance ' + instance + ' is not managed through SSM')
        else:
            raise Exception('Volume ' + volume + ' not currently attached to an instance')
    else:
        print "Change to the Volume {0} is not yet completed; instance will not be tagged for maintenance".format(volume)