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Using AWS Lambda with Amazon CloudWatch Events

Amazon CloudWatch events help you to respond to state changes in your AWS resources. When your resources change state, they automatically send events into an event stream. You can create rules that match selected events in the stream and route them to your AWS Lambda function to take action. For example, you can automatically invoke an AWS Lambda function to log the state of an EC2 instance or AutoScaling group.

CloudWatch Events invokes your function asynchronously with an event document that wraps the event from its source. The following example shows an event that originated from a database snapshot in Amazon Relational Database Service.

Example CloudWatch Events event

{
    "version": "0",
    "id": "fe8d3c65-xmpl-c5c3-2c87-81584709a377",
    "detail-type": "RDS DB Instance Event",
    "source": "aws.rds",
    "account": "123456789012",
    "time": "2020-04-28T07:20:20Z",
    "region": "us-east-2",
    "resources": [
        "arn:aws:rds:us-east-2:123456789012:db:rdz6xmpliljlb1"
    ],
    "detail": {
        "EventCategories": [
            "backup"
        ],
        "SourceType": "DB_INSTANCE",
        "SourceArn": "arn:aws:rds:us-east-2:123456789012:db:rdz6xmpliljlb1",
        "Date": "2020-04-28T07:20:20.112Z",
        "Message": "Finished DB Instance backup",
        "SourceIdentifier": "rdz6xmpliljlb1"
    }
}

You can also create a Lambda function and direct AWS Lambda to invoke it on a regular schedule. You can specify a fixed rate (for example, invoke a Lambda function every hour or 15 minutes), or you can specify a Cron expression.

Example CloudWatch Events message event

{
  "account": "123456789012",
  "region": "us-east-2",
  "detail": {},
  "detail-type": "Scheduled Event",
  "source": "aws.events",
  "time": "2019-03-01T01:23:45Z",
  "id": "cdc73f9d-aea9-11e3-9d5a-835b769c0d9c",
  "resources": [
    "arn:aws:events:us-east-1:123456789012:rule/my-schedule"
  ]
}

To configure CloudWatch Events to invoke your function

  1. Open the Functions page on the Lambda console.

  2. Choose a function

  3. Under Designer, choose Add trigger.

  4. Set the trigger type to CloudWatch Events/EventBridge.

  5. For Rule, choose Create a new rule.

  6. Configure the remaining options and choose Add.

For more information on expressions schedules, see Schedule expressions using rate or cron.

Each AWS account can have up to 100 unique event sources of the CloudWatch Events- Schedule source type. Each of these can be the event source for up to five Lambda functions. That is, you can have up to 500 Lambda functions that can be executing on a schedule in your AWS account.

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