Tutorial: Log the state of an Auto Scaling group using EventBridge - Amazon EventBridge
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Tutorial: Log the state of an Auto Scaling group using EventBridge

You can run an Amazon Lambda function that logs an events whenever an Auto Scaling group launches or terminates an Amazon EC2 instance that indicates whether an event was successful.

For information about more scenarios that use Amazon EC2 Auto Scaling events, see Use EventBridge to handle Auto Scaling events in the Amazon EC2 Auto Scaling User Guide.

In this tutorial, you create a Lambda function, and you create a rule in the EventBridge console that calls that function when an Amazon EC2 Auto Scaling group launches or terminates an instance.


To complete this tutorial, you'll need the following resources:

Step 1: Create a Lambda function

Create a Lambda function to log the scale-out and scale-in events for your Auto Scaling group.

To create a Lambda function
  1. Open the Amazon Lambda console at https://console.amazonaws.cn/lambda/.

  2. Choose Create function.

  3. Choose Author from scratch.

  4. Enter a name for the Lambda function. For example, name the function LogAutoScalingEvent.

  5. Leave the rest of the options as the defaults and choose Create function.

  6. On the Code tab of the function page, double-click index.js.

  7. Replace the existing code with the following code.

    'use strict'; exports.handler = (event, context, callback) => { console.log('LogAutoScalingEvent'); console.log('Received event:', JSON.stringify(event, null, 2)); callback(null, 'Finished'); };
  8. Choose Deploy.

Step 2: Create a rule

Create a rule to run the Lambda function you created in Step 1. The rule runs when your Auto Scaling group starts or stops an instance.

To create a rule
  1. Open the Amazon EventBridge console at https://console.amazonaws.cn/events/.

  2. In the navigation pane, choose Rules.

  3. Choose Create rule.

  4. Enter a name and description for the rule. For example, name the rule TestRule

  5. For Event bus, choose the event bus that you want to associate with this rule. If you want this rule to match events that come from your account, select default. When an Amazon service in your account emits an event, it always goes to your account’s default event bus.

  6. For Rule type, choose Rule with an event pattern.

  7. Choose Next.

  8. For Event source, choose Amazon services.

  9. For Event pattern, do the following:

    1. For Event source, select Auto Scaling from the drop-down list.

    2. For Event type, select Instance Launch and Terminate from the drop-down list.

    3. Choose Any instance event and Any group name.

  10. Choose Next.

  11. For Target types, choose Amazon service.

  12. For Select a target, choose Lambda function from the drop-down list.

  13. For Function, select the Lambda function that you created in the Step 1: Create a Lambda function section. In this example, select LogAutoScalingEvent.

  14. Choose Next.

  15. Choose Next.

  16. Review the details of the rule and choose Create rule.

Step 3: Test the rule

You can test your rule by manually scaling an Auto Scaling group so that it launches an instance. Wait a few minutes for the scale-out event to occur, and then verify that your Lambda function was invoked.

To test your rule using an Auto Scaling group
  1. To increase the size of your Auto Scaling group, do the following:

    1. Open the Amazon EC2 console at https://console.amazonaws.cn/ec2/.

    2. In the navigation pane, choose Auto Scaling, Auto Scaling Groups.

    3. Select the check box for your Auto Scaling group.

    4. On the Details tab, choose Edit. For Desired, increase the desired capacity by one. For example, if the current value is 2, enter 3. The desired capacity must be less than or equal to the maximum size of the group. If your new value for Desired is greater than Max, you must update Max. When you're finished, choose Save.

  2. To view the output from your Lambda function, do the following:

    1. Open the CloudWatch console at https://console.amazonaws.cn/cloudwatch/.

    2. In the navigation pane, choose Logs.

    3. Select the name of the log group for your Lambda function (/aws/lambda/function-name).

    4. Select the name of the log stream to view the data provided by the function for the instance that you launched.

  3. (Optional) When you're finished, you can decrease the desired capacity by one so that the Auto Scaling group returns to its previous size.

Step 4: Confirm success

If you see the Lambda event in the CloudWatch logs, you've successfully completed this tutorial. If the event isn't in your CloudWatch logs, start troubleshooting by verifying the rule was created successfully and, if the rule looks correct, verify the code of your Lambda function is correct.

Step 5: Clean up your resources

You can now delete the resources that you created for this tutorial, unless you want to retain them. By deleting Amazon resources that you are no longer using, you prevent unnecessary charges to your Amazon account.

To delete the EventBridge rule(s)
  1. Open the Rules page of the EventBridge console.

  2. Select the rule(s) that you created.

  3. Choose Delete.

  4. Choose Delete.

To delete the Lambda function(s)
  1. Open the Functions page of the Lambda console.

  2. Select the function(s) that you created.

  3. Choose Actions, Delete.

  4. Choose Delete.