This gist allows you to have a custom service that you can use in automations to delete snapshots from homeassistant. The __init__.py file and the services .yaml file should be put in <path_to_config>/custom_components/clean_up_backups_service. If you are running >= 0.92 version of homeassistant and haven't followed these instructions you will h…

__init__.py

"""
Support for automating the deletion of snapshots.
"""
import logging

import pytz
from dateutil.parser import parse
import asyncio
import aiohttp
import async_timeout
from urllib.parse import urlparse


from homeassistant.const import (CONF_HOST, CONF_TOKEN)
import homeassistant.helpers.config_validation as cv
import voluptuous as vol

_LOGGER = logging.getLogger(__name__)

DOMAIN = 'clean_up_backups_service'
ATTR_NAME = 'number_of_backups_to_keep'
DEFAULT_NUM = 0

CONFIG_SCHEMA = vol.Schema({
    DOMAIN: vol.Schema({
        vol.Required(CONF_HOST): cv.string,
        vol.Required(CONF_TOKEN): cv.string,
        vol.Optional(ATTR_NAME, default=DEFAULT_NUM): int
    }),
}, extra=vol.ALLOW_EXTRA)

async def async_setup(hass, config):
    conf = config[DOMAIN]
    hassio_url = '{}/api/hassio/'.format(conf.get(CONF_HOST))
    auth_token = conf.get(CONF_TOKEN)
    num_snapshots_to_keep = conf.get(ATTR_NAME, DEFAULT_NUM)
    headers = {'authorization': "Bearer {}".format(auth_token)}

    async def async_get_snapshots():
        _LOGGER.info('Calling get snapshots')
        async with aiohttp.ClientSession(raise_for_status=True) as session:
            try:
                with async_timeout.timeout(10, loop=hass.loop):
                    resp = await session.get(hassio_url + 'snapshots', headers=headers, ssl=not isgoodipv4(urlparse(hassio_url).netloc))
                data = await resp.json()
                await session.close()
                return data['data']['snapshots']
            except aiohttp.ClientError:
                _LOGGER.error("Client error on calling get snapshots", exc_info=True)
                await session.close()
            except asyncio.TimeoutError:
                _LOGGER.error("Client timeout error on get snapshots", exc_info=True)
                await session.close()
            except Exception: 
                _LOGGER.error("Unknown exception thrown", exc_info=True)
                await session.close()

    async def async_remove_snapshots(stale_snapshots):
        for snapshot in stale_snapshots:
            async with aiohttp.ClientSession(raise_for_status=True) as session:
                _LOGGER.info('Attempting to remove snapshot: slug=%s', snapshot['slug'])
                # call hassio API deletion
                try:
                    with async_timeout.timeout(10, loop=hass.loop):
                        resp = await session.post(hassio_url + 'snapshots/' + snapshot['slug'] + "/remove", headers=headers, ssl=not isgoodipv4(urlparse(hassio_url).netloc))
                    res = await resp.json()
                    if res['result'].lower() == "ok":
                        _LOGGER.info("Deleted snapshot %s", snapshot["slug"])
                        await session.close()
                        continue
                    else:
                        # log an error
                        _LOGGER.warning("Failed to delete snapshot %s: %s", snapshot["slug"], str(res.status_code))
            
                except aiohttp.ClientError:
                    _LOGGER.error("Client error on calling delete snapshot", exc_info=True)
                    await session.close()
                except asyncio.TimeoutError:
                    _LOGGER.error("Client timeout error on delete snapshot", exc_info=True)
                    await session.close()
                except Exception: 
                    _LOGGER.error("Unknown exception thrown on calling delete snapshot", exc_info=True)
                    await session.close()
    
    def isgoodipv4(s):
        if ':' in s: s = s.split(':')[0]
        pieces = s.split('.')
        if len(pieces) != 4: return False
        try: return all(0<=int(p)<256 for p in pieces)
        except ValueError: return False

    async def async_handle_clean_up(call):
        # Allow the service call override the configuration.
        num_to_keep = call.data.get(ATTR_NAME, num_snapshots_to_keep)
        _LOGGER.info('Number of snapshots we are going to keep: %s', str(num_to_keep))

        if num_to_keep == 0:
            _LOGGER.info('Number of snapshots to keep was zero which is default so no snapshots will be removed')
            return

        snapshots = await async_get_snapshots()
        _LOGGER.info('Snapshots: %s', snapshots) 

        # filter the snapshots
        for snapshot in snapshots:
            d = parse(snapshot["date"])
            if d.tzinfo is None or d.tzinfo.utcoffset(d) is None:
                _LOGGER.info("Naive DateTime found for snapshot %s, setting to UTC...", snapshot["slug"])
                snapshot["date"] = d.replace(tzinfo=pytz.utc).isoformat()
        snapshots.sort(key=lambda item: parse(item["date"]), reverse=True)
        stale_snapshots = snapshots[num_to_keep:]
        _LOGGER.info('Stale Snapshots: {}'.format(stale_snapshots))
        await async_remove_snapshots(stale_snapshots)

    hass.services.async_register(DOMAIN, 'clean_up', async_handle_clean_up)

    return True

automation.yaml

- alias: Daily snapshot clean up
  initial_state: 'on'
  trigger: 
    platform: time
    at: '03:00:00'
  condition:
  action:
    - service: clean_up_backups_service.clean_up
      # Data is optional if you have defined the number of snapshots to keep in the configuration.yaml.
      data:
        # If this property is passed to the service it will be used regardless of what you have in the configuration.yaml
        number_of_backups_to_keep: 7

configuration.yaml

clean_up_backups_service:
  host: !secret base_url
  token: !secret clean_up_token
  number_of_backups_to_keep: 7

services.yaml

clean_up:
  description: Cleans up the snapshots taken by home assistant
  fields:
    number_of_backups_to_keep:
      description: Number of snapshots you wish to keep.
      examle: 3

I don't understand what they mean host and token in configuration.yaml. what needs to be written there?

I don't understand what they mean host and token in configuration.yaml. what needs to be written there?

In your secrets.yaml you write that info.

base_url: The URL that Home Assistant is available on the internet. For example: https://hass-example.duckdns.org:8123. 
clean_up_token: Something like  zte9QkPNevgNuen-OA6NZdLQQmSmJ0BcdA_pQxcMB8Y... created from HA profile page and pasted here

This has been made into a repository and HACS integration You can find the repo here