How do I set up human-readable CloudWatch Events notifications for API calls using input transformers?

Last updated: 2020-07-02

I want to receive human-readable notifications in Amazon CloudWatch Events about Amazon Elastic Compute Cloud (Amazon EC2) security group API calls. How can I use input transformer to set up notifications without receiving the entire JSON log event details?

Short description

You can use event patterns to create an Amazon CloudWatch Events notification for security group-related API calls in your AWS CloudTrail log data. Then, you can use input transformers to convert those events from JSON to a human-readable, customized notification. For more information, see Tutorial: use Input Transformer to customize what is passed to the event target.


Sample event

In the following sample event, a CloudTrail log event is captured when a user creates a security group using CreateSecurityGroup in a virtual private cloud (VPC). This event is then published to CloudWatch in JSON format as follows:

	"version": "0",
	"id": "41dff147-cfbc-492a-9a98-9dd00d082417",
	"detail-type": "AWS API Call via CloudTrail",
	"source": "aws.ec2",
	"account": "123456789012",
	"time": "2017-07-14T16:36:23Z",
	"region": "us-east-1",
	"resources": [],
	"detail": {
		"eventVersion": "1.05",
		"userIdentity": {
			"type": "Root",
			"principalId": "123456789012",
			"arn": "arn:aws:iam::123456789012:root",
			"accountId": "123456789012",
			"accessKeyId": "ASIAIRP4G1234567891Q",
			"userName": "iamuser",
			"sessionContext": {
				"attributes": {
					"mfaAuthenticated": "false",
					"creationDate": "2017-07-14T16:27:38Z"
		"eventTime": "2017-07-14T16:36:23Z",
		"eventSource": "",
		"eventName": "CreateSecurityGroup",
		"awsRegion": "us-east-1",
		"sourceIPAddress": "",
		"userAgent": "",
		"requestParameters": {
			"groupName": "test",
			"groupDescription": "test",
			"vpcId": "vpc-54a4232d"
		"responseElements": {
			"_return": true,
			"groupId": "sg-82d531f3"
		"requestID": "a4609e55-69ac-4a2d-8057-843dc8b4658b",
		"eventID": "7774b898-59c1-48a5-9c41-af1bcaa04612",
		"eventType": "AwsApiCall"

Example resolution

Use the following example resolution as a model for creating your own custom, human-readable notifications from CloudWatch Events in JSON format.

1.    Create a CloudWatch Events rule for security group-related API calls. For Event Pattern, choose Build custom event pattern. Be sure to modify the sample event pattern for your use case. Note that while the example notification is for CreateSecurityGroup, the following sample event pattern includes all security group-related API call actions:

  "source": [
  "detail-type": [
    "AWS API Call via CloudTrail"
  "detail": {
    "eventSource": [
    "eventName": [

2.    For your rule's Target, choose Input Transformer under Configure input.

3.    In the first input box, configure your Input Path. Include any key-value pairs to be used in your notification. Be sure to modify the following sample input path for your use case:


Note: CloudWatch Events currently supports a maximum of 10 variables in input path maps. To extract more than 10 variables, pass the entire event to an AWS Lambda function for parsing. Then, construct a message body in the required format for publication to Amazon Simple Notification Service (Amazon SNS).

4.    In the second input box, configure the Input Template. Include a string with placeholders for values from your input path. This string is the human-readable text of your notification. Be sure to modify the following sample input template for your use case:

"User <user>  has executed API call <action> from source IP <sourceip> on security group <sgid>/<sgname> that belongs to vpc <vpcid> in region <region> at time(UTC) <time>. The Request ID is <reqid>."

Note: If you receive an Invalid InputTemplate error when saving a template with line breaks, be sure to close each line with double quotation marks. For example:

"<type> <arn> has executed action API <action> on Security Group <sgid> located in AWS region <region> at <time> (UTC)."
"Event Details:"
"Request ID: <requestid>"
"Event ID: <eventid>"
"Event Source: <eventsource>"
"Event Type: <eventtype>"

5.    Choose Configure details.

6.    Specify a name and description for the rule.

7.    Choose Create rule.

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