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@aws-cdk/aws-events v0.28.0

AWS CloudWatch Events Construct Library

AWS CloudWatch Events Construct Library

Amazon CloudWatch Events delivers a near real-time stream of system events that describe changes in AWS resources. For example, an AWS CodePipeline emits the State Change event when the pipeline changes it's state.

  • Events: An event indicates a change in your AWS environment. AWS resources can generate events when their state changes. For example, Amazon EC2 generates an event when the state of an EC2 instance changes from pending to running, and Amazon EC2 Auto Scaling generates events when it launches or terminates instances. AWS CloudTrail publishes events when you make API calls. You can generate custom application-level events and publish them to CloudWatch Events. You can also set up scheduled events that are generated on a periodic basis. For a list of services that generate events, and sample events from each service, see CloudWatch Events Event Examples From Each Supported Service.
  • Targets: A target processes events. Targets can include Amazon EC2 instances, AWS Lambda functions, Kinesis streams, Amazon ECS tasks, Step Functions state machines, Amazon SNS topics, Amazon SQS queues, and built-in targets. A target receives events in JSON format.
  • Rules: A rule matches incoming events and routes them to targets for processing. A single rule can route to multiple targets, all of which are processed in parallel. Rules are not processed in a particular order. This enables different parts of an organization to look for and process the events that are of interest to them. A rule can customize the JSON sent to the target, by passing only certain parts or by overwriting it with a constant.

The EventRule construct defines a CloudWatch events rule which monitors an event based on an event pattern and invoke event targets when the pattern is matched against a triggered event. Event targets are objects that implement the IEventTarget interface.

Normally, you will use one of the source.onXxx(name[, target[, options]]) -> EventRule methods on the event source to define an event rule associated with the specific activity. You can targets either via props, or add targets using rule.addTarget.

For example, to define an rule that triggers a CodeBuild project build when a commit is pushed to the "master" branch of a CodeCommit repository:

const onCommitRule = repo.onCommit('OnCommitToMaster', project, 'master');

You can add additional targets, with optional input transformer using eventRule.addTarget(target[, input]). For example, we can add a SNS topic target which formats a human-readable message for the commit.

For example, this adds an SNS topic as a target:

onCommitRule.addTarget(topic, {
    template: 'A commit was pushed to the repository <repo> on branch <branch>',
    pathsMap: {
        branch: '$.detail.referenceName',
        repo: '$.detail.repositoryName'
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