Lambda_invoke.py

##Import Libraries
import json
import boto3
import jmespath

## Recieve event from Cloud watch Event bus
## Variable "ID" get the instance id which triggered the alert.
## Variable "Sourceaccount" gets the account information from where the Cloudwatch rule triggered.
def lambda_handler(event, context):
  print('Input received:')
  print(json.dumps(event, indent=4))
  print('Instance ID:', event['detail']['requestParameters']['instancesSet']['items'][0]['instanceId'])
  ID = ('Instance ID:', event['detail']['requestParameters']['instancesSet']['items'][0]['instanceId'])
  print(ID)
  Sourceaccount = event['account']
  print('Sourceaccount',Sourceaccount)
  
## AssumeRole
## replace "cross-accounrole" in Line 22 with your role created in each account
  sts_connection = boto3.client('sts')
  acct_b = sts_connection.assume_role(
        RoleArn='arn:aws:iam::' + Sourceaccount + ':role/cross-account-role', 
        RoleSessionName='cross_acct_lambda'
   )
    
  ACCESS_KEY = acct_b['Credentials']['AccessKeyId']
  SECRET_KEY = acct_b['Credentials']['SecretAccessKey']
  SESSION_TOKEN = acct_b['Credentials']['SessionToken']

 
## Get the tag information
  ec2_client = boto3.client('ec2', region_name='us-east-2',
        aws_access_key_id=ACCESS_KEY,
        aws_secret_access_key=SECRET_KEY,
        aws_session_token=SESSION_TOKEN,)
  Inst = [event['detail']['requestParameters']['instancesSet']['items'][0]['instanceId']]
  print(Inst)
  myinstance = ec2_client.describe_instances(InstanceIds = Inst)
  GetTag = (jmespath.search("Reservations[].Instances[].[Tags[?Key=='Name'].Value]",myinstance))
  Tag = (GetTag[0][0][0])
  print(Tag)