Listerners and Rules alarm

Hello.

From CloudWatch metrics, open "Usage" → "AWS Resource" and check the "ListenersPerApplicationLoadBalancer" metric to see the maximum number of listeners associated with the ALB in that region.
Therefore, I think creating an alarm on this metric will accomplish this goal.
You can also see the number of target groups associated with an ALB using the metric "TargetGroupsPerApplicationLoadBalancer".
https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/CloudWatch-Quotas-Visualize-Alarms.html

Yes, you can create a CloudWatch alarm to monitor when load balancer listener rules across all your load balancers are approaching their limit.

To set this up, you would need to:

1. Open the CloudWatch console
2. Navigate to Alarms > All Alarms
3. Choose Create alarm
4. Select the appropriate metric for load balancer listener rules
5. Set the statistic (such as Average or Maximum)
6. Define your threshold (for example, > 80 or > 90 to give you advance warning before reaching 100)
7. Configure the period and evaluation periods
8. Set up notifications by selecting or creating an SNS topic to receive alerts when the alarm state changes
9. Provide a name and description for your alarm
10. Complete the alarm creation

You can also configure how the alarm should handle missing data and low sample counts. For notifications, you can have the alarm send multiple notifications for the same alarm state or for different alarm states.

If you're using AWS Managed Services (AMS) Accelerate, there are default monitoring configurations for load balancers that you can customize through a configuration document or service request.
Sources
Create a load balancer latency alarm that sends email - Amazon CloudWatch
Create a CloudWatch alarm based on a static threshold - Amazon CloudWatch
Alerts from baseline monitoring in AMS - AMS Accelerate User Guide