How can I send events to EventBridge upon AWS CloudWatch alarm status change?

How to send an Event to EventBridge on Alarm state change?

Alarm events and EventBridge - Amazon CloudWatch says it's possible but doesn't tell how to.

UI Actions available on alarm also doesn't let EventBridge to be set as an action.

I don't want to use SNS. I need to trigger specifically via EventBridge.

EventBridge cannot be a target for the Alarm. Instead, EventBridge is the bus that receives all the events from AWS (and optionally from AWS Partners and your custom events). That being said, in order to catch the Alarm from Cloudwatch into EventBridge, you have to go to:

EventBridge->Rules->Create rule

In Event source, choose AWS events or EventBrige partner events

In Sample event you can choose CloudWatch Alarm State Change so you can see a full list of values that you can use to filter your events.

In Event pattern you will choose:

AWS services -> CloudWatch -> CloudWatch Alarm State Change

This will create an Event pattern like this:

{
  "source": ["aws.cloudwatch"],
  "detail-type": ["CloudWatch Alarm State Change"]
}

You will want to set it for specific alarm and state, so you should add at least resource and detail.state sections, something like:

{
  "source": ["aws.cloudwatch"],
  "detail-type": ["CloudWatch Alarm State Change"],
  "resources": ["arn:aws:cloudwatch:us-east-1:123456789012:alarm:ServerCpuTooHigh"],
  "detail": {
    "state": {
      "value": ["ALARM"]
    }
  }
}