Adjust cron events for DST (Daylight Savings Time) automatically with a Python function to be run on AWS Lambda.

adjust-cron-for-dst.py

from datetime import datetime
import pytz
import boto3

# define our CloudEvents client
client = boto3.client('events')

# Let's grab our current time in GMT and convert it to local time (US Central)
utc_time = datetime.utcnow().replace(tzinfo=pytz.utc)
# Set your timezone here! See timezones here: https://gist.github.com/heyalexej/8bf688fd67d7199be4a1682b3eec7568
cst_timezone = pytz.timezone('US/Central')
cst_time = utc_time.astimezone(cst_timezone)

# This will show the offset in seconds for DST ⏰
# If it's zero, we're not in DST
is_dst = cst_time.tzinfo._dst.seconds != 0

# Determine our new cron expressions for a function running every day at 7am and 7pm CST
# Adjust these times to fit what you would like for during and after of DST
if is_dst:
  start_schedule = 'cron(0 12 ? * * *)'
  stop_schedule = 'cron(0 0 ? * * *)'
else:
  start_schedule = 'cron(0 13 ? * * *)'
  stop_schedule = 'cron(0 1 ? * * *)'

# Set the names of your AWS Event rules here
START_RULE = "start_rule"
STOP_RULE = "stop_rule"

# Fetch the targets of our current cron rules
start_settings = client.list_targets_by_rule(Rule=START_RULE)
stop_settings = client.list_targets_by_rule(Rule=STOP_RULE)

# Remove targets from current rules
client.remove_targets(
  Rule=START_RULE,
  Ids=[(start_settings['Targets'][0]['Id'])]
)
client.remove_targets(
  Rule=STOP_RULE,
  Ids=[(stop_settings['Targets'][0]['Id'])]
)

# Delete rules
client.delete_rule(Name=START_RULE)
client.delete_rule(Name=STOP_RULE)

# Add new rules
client.put_rule(
  Name=START_RULE,
  ScheduleExpression=start_schedule,
  State='ENABLED',
  Description="Automatic trigger for the function."
)
client.put_rule(
  Name=STOP_RULE,
  ScheduleExpression=stop_schedule,
  State='ENABLED',
  Description="Automatic trigger for the function"
)

# Add back our targets
client.put_targets(
  Rule=START_RULE,
  Targets=[
    {
      'Id': start_settings['Targets'][0]['Id'],
      'Arn':start_settings['Targets'][0]['Arn'],
      'Input': start_settings['Targets'][0]['Input']
    }
  ]
)
client.put_targets(
  Rule=STOP_RULE,
  Targets=[
    {
      'Id': stop_settings['Targets'][0]['Id'],
      'Arn':stop_settings['Targets'][0]['Arn'],
      'Input': stop_settings['Targets'][0]['Input']
    }
  ]
)