Lambda/boto3/python loop - python-3.x

Question

This code acts as an early warning system for ADFS failures, which works fine when run locally. Problem is that when I run it in Lambda, it loops non stop.
In short:
lambda_handler() runs pagecheck()
pagecheck() produces the info needed then passes 2 lists (msgdet_list, error_list) and an int (error_count) to notification().
notification() collates and prints the output. The output is two key variables (notificationheader and notificationbody).
I've #commentedOut the SNS piece which would usually email the info, and am using print() to instead send the info to CloudWatch logs until I can get the loop sorted. Logs:
CloudWatch logs
If I run this locally, it produces a clean single output. In Lambda, the function will loop until it times out. It's almost like every time the lists are updated, they're passed to the notification() module and it's run. I can limit the function time, but would rather fix the code!
Cheers,
tac
# This python/boto3/lambda script sends a request to an Office 365 landing page, parses return details to confirm a successful redirect to /
# the organisation ADFS homepage, authenticates homepge is correct, raises any errors, and sends a consolodated report to /
# an AWS SNS topic.
# Run once to produce pageserver and htmlchar values for global variables.
# Import required modules
import boto3
import urllib.request
from urllib.request import Request, urlopen
from datetime import datetime
import time
import re
import sys
# Global variables to be set
url = "https://outlook.com/CONTOSSO.com"
adfslink = "https://sts.CONTOSSO.com/adfs/ls/?client-request-id="
# Input after first run
pageserver = "Microsoft-HTTPAPI/2.0 Microsoft-HTTPAPI/2.0"
htmlchar = 18600
# Input AWS SNS ARN
snsarn = 'arn:aws:sns:ap-southeast-2:XXXXXXXXXXXXX:Daily_Check_Notifications_CONTOSSO'
sns = boto3.client('sns')
def pagecheck():
# Present the request to the webpage as if coming from a user in a browser
user_agent = 'Mozilla/5.0 (Windows NT 6.1; Win64; x64)'
values = {'name' : 'user'}
headers = { 'User-Agent' : user_agent }
data = urllib.parse.urlencode(values)
data = data.encode('ascii')
# "Null" the Message Detail and Error lists
msgdet_list = []
error_list = []
request = Request(url)
req = urllib.request.Request(url, data, headers)
response = urlopen(request)
with urllib.request.urlopen(request) as response:
# Get the URL. This gets the real URL.
acturl = response.geturl()
msgdet_list.append("\nThe Actual URL is:")
msgdet_list.append(str(acturl))
if adfslink not in acturl:
error_list.append(str("Redirect Fail"))
# Get the HTTP resonse code
httpcode = response.code
msgdet_list.append("\nThe HTTP code is: ")
msgdet_list.append(str(httpcode))
if httpcode//200 != 1:
error_list.append(str("No HTTP 2XX Code"))
# Get the Headers as a dictionary-like object
headers = response.info()
msgdet_list.append("\nThe Headers are:")
msgdet_list.append(str(headers))
if response.info() == "":
error_list.append(str("Header Error"))
# Get the date of request and compare to UTC (DD MMM YYYY HH MM)
date = response.info()['date']
msgdet_list.append("The Date is: ")
msgdet_list.append(str(date))
returndate = str(date.split( )[1:5])
returndate = re.sub(r'[^\w\s]','',returndate)
returndate = returndate[:-2]
currentdate = datetime.utcnow()
currentdate = currentdate.strftime("%d %b %Y %H%M")
if returndate != currentdate:
date_error = ("Date Error. Returned Date: ", returndate, "Expected Date: ", currentdate, "Times in UTC (DD MMM YYYY HH MM)")
date_error = str(date_error)
date_error = re.sub(r'[^\w\s]','',date_error)
error_list.append(str(date_error))
# Get the server
headerserver = response.info()['server']
msgdet_list.append("\nThe Server is: ")
msgdet_list.append(str(headerserver))
if pageserver not in headerserver:
error_list.append(str("Server Error"))
# Get all HTML data and confirm no major change to content size by character lenth (global var: htmlchar).
html = response.read()
htmllength = len(html)
msgdet_list.append("\nHTML Length is: ")
msgdet_list.append(str(htmllength))
msgdet_list.append("\nThe Full HTML is: ")
msgdet_list.append(str(html))
msgdet_list.append("\n")
if htmllength // htmlchar != 1:
error_list.append(str("Page HTML Error - incorrect # of characters"))
if adfslink not in str(acturl):
error_list.append(str("ADFS Link Error"))
error_list.append("\n")
error_count = len(error_list)
if error_count == 1:
error_list.insert(0, 'No Errors Found.')
elif error_count == 2:
error_list.insert(0, 'Error Found:')
else:
error_list.insert(0, 'Multiple Errors Found:')
# Pass completed results and data to the notification() module
notification(msgdet_list, error_list, error_count)
# Use AWS SNS to create a notification email with the additional data generated
def notification(msgdet_list, error_list, errors):
datacheck = str("\n".join(msgdet_list))
errorcheck = str("\n".join(error_list))
notificationbody = str(errorcheck + datacheck)
if errors >1:
result = 'FAILED!'
else:
result = 'passed.'
notificationheader = ('The daily ADFS check has been marked as ' + result + ' ' + str(errors) + ' ' + str(error_list))
if result != 'passed.':
# message = sns.publish(
# TopicArn = snsarn,
# Subject = notificationheader,
# Message = notificationbody
# )
# Output result to CloudWatch logstream
print('Response: ' + notificationheader)
else:
print('passed')
sys.exit()
# Trigger the Lambda handler
def lambda_handler(event, context):
aws_account_ids = [context.invoked_function_arn.split(":")[4]]
pagecheck()
return "Successful"
sys.exit()

Answer 1

Your CloudWatch logs contain the following error message:
Process exited before completing request
This is caused by invoking sys.exit() in your code. Locally your Python interpreter will just terminate when encountering such a sys.exit().
AWS Lambda on the other hand expects a Python function to just return and handles sys.exit() as an error. As your function probably got invoked asynchronously AWS Lambda retries to execute it twice.
To solve your problem, you can replace the occurences of sys.exit() with return or even better, just remove the sys.exit() calls, as there would be already implicit returns in the places where you use sys.exit().