Shutdown EC2 instances off hours with AWS Lambda + Serverless framework + Python

handler.py

import boto3
region = 'us-east-1'

def find_instance_ids(ec2):
    response = ec2.describe_instances(Filters=[
        {'Name': "tag:StopOffHours", 'Values': ["yes"]}
    ])
    return [
        instance['InstanceId'] 
        for reservation in response['Reservations']
        for instance in reservation['Instances']
    ]

def stop(event, context):
    ec2 = boto3.client('ec2', region_name=region)
    instance_ids = find_instance_ids(ec2)
    print("Stopping instances: " + str(instance_ids))
    ec2.stop_instances(InstanceIds=instance_ids)

def start(event, context):
    ec2 = boto3.client('ec2', region_name=region)
    instance_ids = find_instance_ids(ec2)
    print("Starting instances: " + str(instance_ids))
    ec2.start_instances(InstanceIds=instance_ids)

serverless.yml

service: my-scheduler
provider:
  name: aws
  runtime: python3.7
  region: us-east-1
  iamRoleStatements:
    - Effect: Allow
      Action:
        - ec2:Describe*
      Resource:
        - "*"
    - Effect: Allow
      Action:
        - ec2:StartInstances
        - ec2:StopInstances
      Resource:
        - arn:aws:ec2:*:*:instance/*
      Condition:
        StringEquals:
          "ec2:ResourceTag/StopOffHours": "yes"
package:
  exclude:
    - "**/*"
  include:
    - "!./**"
    - handler.py
functions:
  StopOffHours:
    handler: handler.stop
    events:
      - schedule: cron(0 23 ? * MON-FRI *)
  StartDuringHours:
    handler: handler.start
    events:
      - schedule: cron(0 13 ? * MON-FRI *)
plugins:
  - serverless-python-requirements