AWS Lambda Serverless Computing with EC2, CloudWatch Alarm, SNS

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Lambda function triggered by EC2 instance launch

In this section, we'll learn how to use lambda function with CloudWatch Events to react EC2 launch.

Let's create a lambda function:

Here is the policy attached to "lambda_micro_role":

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Action": [
                "logs:createLogGroup"
            ],
            "Resource": "arn:aws:logs:us-east-1:526262051452:*",
            "Effect": "Allow"
        },
        {
            "Action": [
                "logs:createLogStream",
                "logs:PutLogEvents"
            ],
            "Resource": "arn:aws:logs:us-east-1:526262051452:log-group:*",
            "Effect": "Allow"
        }
    ]
}

The role gives our lambda function basic permissions to respond to log events to EC2 instance.

Click "Create function".

We need a new code to receive events and log the events to a log file:

exports.handler = function(event, context)
{
  console.log("MonitorEC2()");
  console.log("Here's the event:\n:"+JSON.stringify(event, null, 4));
  context.succeed("Ready!");
};

Once pasted the code, click "Save".

Now, we want to trigger the lambda function whenever an EC2 instance is launched (actually, when it is in running status). So, we need to setup CloudWatch Events rule.

Note that we configured the activity of the rule by setting the trigger target as the lambda function, "EC2-Monitor".

To configure details of the rule, click "Configure details":

Click "Create rule":

To test our CloudWatch Event rule and the lambda function, let's launch an instance with Amazon Linux AMI.

Then, go to our lambda function, "EC2-monitor", and click the "Monitoring" tab.

Click "View logs in CloudWatch":

Lambda function with SNS - checking site content

In this section, we'll create a lambda function from the AWS blueprint called "lambda-canary".

It will check if a site has txt string. If not our lambda function throws an error.

Picture source: https://amazon.qwiklabs.com

Click "Configure"

The function code:

from __future__ import print_function

import os
import urllib2
from datetime import datetime

SITE = os.environ['site']  # 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


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:
        opener = urllib2.build_opener()
        opener.addheaders = [('User-Agent', 'AWS Lambda')]
        if not validate(opener.open(SITE).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())))

Click "Create function".

Time to test.

Click "Create" button at the bottom of the screen.

Click "Test":

Now, let's setup a notification service (SNS). When an alarm is triggered, we'll receive an email. We receive a notification via SNS by subscribing to the topic (email subscription) whenever a message is sent to the topic.

We need to create a SNS topic:

Once we confirm the email subscription, the SNS is now ready to receive messages from CloudWatch Alarm which will be triggered when the Web site check fails.

Let's setup the CloudWatch Alarm.