Technical references: March 2018

Check website with AWS Lambda using Python 2.7

Create SNS topic

Go to SNS
Create Topic

Topic name: Check_Website
Display name: checksite

Subscribe yourself to this topic

Take note of the Topic ARN

Create IAM Policy

Go to IAM
Select Policies
Create Policy

Service: SNS
Action: ALL (*)
Resource: Specific, enter ARN from SNS topic created in previous step

Review policy
Name: publish_check_website
Create Policy

Take note of the Policy ARN

Create the appropriate role

Go to IAM
Select Roles
Create Role
Select AWS service
Select Lambda
Click Next: Permissions
Add AWSLambdaBasicExecutionRole
Add publish_check_website
Next: Review
Role Name: Lambda_SNS
Create Role

Create Lambda Function

Go to Lambda
Select Create Function
Select Blueprints
Filter on term, "lambda-canary" and select the blueprint
Select Configure
Basic Information

Name: website-check
Role: Choosing an existing role
Existing role: Lambda_SNS

cloudwatch-events

Rule: Create a new rule
Rule name: daily_website_check
Rule type: schedule expression
Schedule Expression: cron(0 10 * * ? *) Ref

Enable trigger
Create function

Update Code

from __future__ import print_function

import os
import json
import boto3
from botocore.vendored import requests
from datetime import datetime
from urllib2 import urlopen

SITES = os.environ['sites']  # URL of the site to check, stored in the site environment variable, e.g. https://aws.amazon.com
EXPECTED = os.environ['expected']  # String expected to be on the page, stored in the expected environment variable, e.g. Amazon
SNS_ARN = os.environ['sns_arn']


sites_array = SITES.split(';')
expec_array = EXPECTED.split(';')

def validate(res,exp):
    '''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 exp in res

def lambda_handler(event, context):
    this_message = "Website Check Script\r\n"
    this_message = this_message + datetime.now().strftime('%m/%d/%Y %H:%M')
    this_message = this_message + "(UTC) \r\n"
    for i in range(len(sites_array)):
        this_message = this_message + 'Checking ' + sites_array[i] + ": "
        try:
            if not validate(urlopen(sites_array[i]).read(),expec_array[i]):
                raise Exception('Validation failed')
        except:
            this_message = this_message + 'Check Failed ' + "\r\n"
        else:
            this_message = this_message + 'Check Success ' + "\r\n"
            
            
    url = 'https://icanhazdadjoke.com/'
    headers = {'Accept': 'text/plain'}
    r = requests.get(url, headers=headers)
    print(r.text)
    this_message = this_message + "\r\b" + r.text + "\r\n"
    
    client = boto3.client('sns')
    response = client.publish(
        TargetArn=SNS_ARN,
        Message=this_message,
        MessageStructure='text'
    )

Update Environment Variables

Update the keys to as follows:
Values for expected and sites must be semi-colon separated. List of expected must be any unique string(s) that exists on the page