Detecting events with CloudWatch 

Using Amazon CloudWatch, we will first create a rule that detects when an EC2 instance state changes to a running state. Follow these steps:

1. From the Amazon CloudWatch dashboard, select Rules under Events from the left menu:

2. Next, select Create Rule, and the following screen will be displayed:

3. Using the drop-down list, select EC2 for Service Name.

4. For Event Type, you can select EC2 Instance State-change Notification:

5. Select running under the Specific state(s) drop-down list.
6. Select Any instance. Your event pattern is now configured to record any events where an EC2 instance is listed as running, and this can be seen under Event Pattern Preview:

Now that you have identified which event(s) you want to capture, you need to configure the response to those events.