AWS > Lambda > Canary Function - amazon-web-services

Question

I am looking to use a Lambda function to monitor multiple websites, how would you alter the below codes (from BluePrint)?
Multiple env variable can be set up (e.g. site2, expected2), I just need help with making them work inside the function.
Thank you.
import os
from datetime import datetime
from urllib.request import Request, urlopen
SITE = os.environ['site'] # URL of the site to check, stored in the site environment variable
EXPECTED = os.environ['expected'] # String expected to be on the page, stored in the expected environment variable
def validate(res):
'''Return False to trigger the canary
Currently this simply checks whether the EXPECTED string is present.
However, you could modify this to perform any number of arbitrary
checks on the contents of SITE.
'''
return EXPECTED in res
def lambda_handler(event, context):
print('Checking {} at {}...'.format(SITE, event['time']))
try:
req = Request(SITE, headers={'User-Agent': 'AWS Lambda'})
if not validate(str(urlopen(req).read())):
raise Exception('Validation failed')
except:
print('Check failed!')
raise
else:
print('Check passed!')
return event['time']
finally:
print('Check complete at {}'.format(str(datetime.now())))

Answer 1

Several ways to go here, but rather than adding new envars for each site and expected value, you could just use two envvars to hold lists. Then in the lambda function, split the lists, zip them together into a dictionary, and iterate through the dict items using the key and value to call your modified validate() function.
Something like
import os
from datetime import datetime
from urllib.request import Request, urlopen
SITES = os.environ['sites'] # comma-separated URLs of the sites to check, stored in the site environment variable
EXPECTED_VALUES = os.environ['expected_values'] # comma-separated strings expected to be o site's page, stored in the expected environment variable
sites = SITES.split(',')
expected_values = EXPECTED_VALUES.split(',')
sites_to_check = dict(zip( sites,expected_values)
def validate(page_content, expected_value):
'''Return False to trigger the canary
Currently this simply checks whether the EXPECTED string is present.
However, you could modify this to perform any number of arbitrary
checks on the contents of SITE.
'''
return expected_value in page_content
def lambda_handler(event, context):
for site in sites_to_check.items():
url = site(0)
expected_val = site(1)
print('Checking {} at {}...'.format(url, event['time']))
try:
req = Request(url, headers={'User-Agent': 'AWS Lambda'})
if not validate(str(urlopen(req).read()), expected_val):
raise Exception('Validation failed')
except:
print('Check failed!')
raise
else:
print('Check passed!')
# keep on looping until we get through them all
finally:
print('Check complete for {} at {}'.format(url, str(datetime.now())))
# if we got here, we checked all the sites and they passed
print('Checked all sites and they all passed at {}'.format(str(datetime.now())))
I have not run or tested this code, but you get the idea - make it a loop!