This snapshot will keep on creating the snaps of EC2 instances having the TAGS as "backup"="true". But you have to schedule when to take snaps in the CloudWatch Event Rule. Also this will keep on creating the snap so REMEMBER to implement PruneSnapShots lambda function when you use this CreateSnapShot function to delete the snapshot created and …

CreateSnapShot.py

from datetime import datetime
import boto3

def lambda_handler(event, context):

    ec2_client = boto3.client('ec2')
    regions = [region['RegionName']
               for region in ec2_client.describe_regions()['Regions']]

    for region in regions:

        print('Instances in EC2 Region {0}:'.format(region))
        ec2 = boto3.resource('ec2', region_name=region)

        instances = ec2.instances.filter(
            Filters=[ {'Name': 'tag:backup', 'Values': ['true']}
            ]
            )

# ISO 8601 timestamp, i.e. 2019-01-31T14:01:58
        timestamp = datetime.utcnow().replace(microsecond=0).isoformat() 

        for i in instances.all():
            for v in i.volumes.all():
                desc = 'Backup of {0}, volume {1}. created {2}'.format(i.id, v.id, timestamp)

                print(desc)

                snapshot = v.create_snapshot(Description=desc)

                print("Created snapshot:", snapshot.id)