Email notification through SNS and Lambda

Question

I am facing an issue. My main motive is to send an email whenever there is state change happened to ec2 instances.

I tried cloud watch events directly with SNS and its work also but the email template which I am receiving is not having the proper information to understood.

I was expecting Server name and its IP in the email template which SNS does not give me the option to modify it. So What I am thinking is to involve lambda so that

• cloudwatch events to monitor EC2 instances state change and
• give input to Lambda which will have customized email template which is
• then invoke SNS to send email to recipients.

Let me know if you think this is correct method for what I am expecting or not. and give some insights on how to get Lambda in between Cloud watch and SNS

Thanks & Regards

Answer 1

As shown in the Amazon CloudWatch Events console, a sample event triggered by an instance state change is:

{
  "version": "0",
  "id": "7bf73129-1428-4cd3-a780-95db273d1602",
  "detail-type": "EC2 Instance State-change Notification",
  "source": "aws.ec2",
  "account": "123456789012",
  "time": "2015-11-11T21:29:54Z",
  "region": "us-east-1",
  "resources": [
    "arn:aws:ec2:us-east-1:123456789012:instance/i-abcd1111"
  ],
  "detail": {
    "instance-id": "i-abcd1111",
    "state": "pending"
  }
}

CloudWatch events can then directly trigger an AWS Lambda function, passing in this information.

The Lambda function can use the Instance ID to retrieve further details about the instance (eg server name, IP address).

The function can then either:

• Send text to an Amazon SNS Topic, which can forward the information to subscribers (via email or SMS), OR
• Send the emails via Amazon Simple Email Service (SES), which can send emails with complex formatting

Using SNS would be the easiest, if you don't mind the text-based content.

Here is some sample code that will receive an event from Amazon CloudWatch Events when an instance changes state, then send a message to an Amazon SNS topic with further details:

import boto3

def lambda_handler(event, context):

    # Extract Instance ID from event
    instance_id = event['detail']['instance-id']

    # Obtain information about the instance
    ec2_client = boto3.client('ec2')
    instance_info = ec2_client.describe_instances(InstanceIds=[instance_id])
    instance = instance_info['Reservations'][0]['Instances'][0]

    # Extract name tag
    name_tags = [t['Value'] for t in instance['Tags'] if t['Key']=='Name']
    name = name_tags[0] if name_tags is not None else ''

    # Send message to SNS
    MY_SNS_TOPIC_ARN = 'arn:aws:sns:ap-southeast-2:123456789012:foo'
    sns_client = boto3.client('sns')
    sns_client.publish(
        TopicArn = MY_SNS_TOPIC_ARN,
        Subject = 'Instance Change State: ' + instance_id,
        Message = 'Instance: ' + instance_id + ' has changed state\n' +
                  'State: ' + instance['State']['Name'] + '\n' +
                  'IP Address: ' + instance['PublicIpAddress'] + '\n' +
                  'Name: ' + name
    )

To setup:

• Create an SNS topic to receive the message and put the topic ARN in the code
• Create a subscriber to the SNS topic (easiest is via SMS when testing)
• Create the AWS Lambda function (shown above)
• Create an Amazon CloudWatch Event to trigger off EC2 instance state change, and set the target to the Lambda function