I'm working on a project that involves auto-scaling groups where instances are frequently terminated and created. To monitor these instances, I use a Lambda function triggered by EventBridge to gather custom metrics through the CloudWatch agent. My approach involves fetching the instance information and retrieving the tags for each instance to use their names for creating alarms.
I've set up a fallback mechanism to use the instance ID in the alarm name if the instance name isn't set, but ideally, the name should be assigned through the user data script. However, I still encounter a few alarms that show instance IDs instead of names. I'm wondering what could be causing this issue and how I can prevent it.
2 Answers
I totally feel you on this! If your Lambda is already checking again after 60 seconds and it's still using instance IDs, you might want to explore delaying the entire UserData script. This way, you can ensure that the tag is set before the Lambda kicks in. Check out if there are ways to control the sequence of events in your stack that might help. More control might help you avoid the ID fallback.
It sounds like you might be dealing with a race condition since the UserData script executes after the instance is up and running. One solution could be to tweak your Lambda function to add a brief pause before it checks for the name tag. If it doesn't find one, you could retry after waiting a couple of seconds. You might also want to consider setting a maximum number of retries before it defaults to the instance ID, just in case the name is never set.
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