[SOLVED] Trigger script automatically on EC2 creation (no user data)

Issue

Everytime an EC2 instance gets created, I want to run a script on that instance. I understand this could be done using the user_data parameter but some of these instances get created manually so people may forget to fill in that parameter sometimes. I want to rely on something automatic instead.

I figured to do it with EventBridge, catch an event that would indicate me that an instance has been created then trigger a lambda that would run the script. But when looking in the documentation I couldn't find any event that would relate to "EC2 created", see https://docs.aws.amazon.com/AWSEC2/latest/WindowsGuide/monitoring-instance-state-changes.html.

Any idea how to get this done?

Solution

Create an EventBridge rule with the following pattern to catch the event:

{
  "source": ["aws.ec2"],
  "detail-type": ["AWS API Call via CloudTrail"],
  "detail": {
    "eventSource": ["ec2.amazonaws.com"],
    "eventName": ["RunInstances"]
  }
}

and configure the target of the rule to be an AWS lambda function. Configure the lambda to parse the event and invoke an SSM run command against the instance.

Answered By - Paolo

Answer Checked By - Willingham (WPSolving Volunteer)