Answer
An event pattern is a JSON structure that describes the specific characteristics of events you want a rule to match, such as a particular event source, a specific detail type, or particular values within the event's data, and only events that match this pattern are forwarded to the targets configured for that rule, letting you precisely filter which events trigger which actions.
{
"source": ["aws.ec2"],
"detail-type": ["EC2 Instance State-change Notification"],
"detail": { "state": ["stopped"] }
}Real-world example An operations team creates an EventBridge rule with an event pattern that only matches EC2 instances entering a stopped state, triggering an automated notification only for that specific scenario rather than every possible EC2 event.