import boto3
import os
import json

# reference: https://aws.amazon.com/premiumsupport/knowledge-center/start-stop-lambda-eventbridge/

def lambda_handler(event, context):
    ec2 = boto3.client('ec2', region_name=os.environ['region_name'])
    instances = json.loads(os.environ['instances'])
    if event['action'] == 'start':
        resp = ec2.start_instances(InstanceIds=instances)
    elif event['action'] == 'stop':
        resp = ec2.stop_instances(InstanceIds=instances)
    else:
        raise ValueError("Invalid event action")
    return resp