AppRunner CloudWatch Alarm not showing metrics

Question

I'm trying to create an alarm for AppRunner. My AppRunner service is running fine.

It keeps showing "Insufficient data". I'm using Terraform, but weirdly enough, creating an alarm manually also results in the same no data message. I've tried memory metrics but same thing. Any ideas?

```terraform
resource "aws_cloudwatch_metric_alarm" "apprunner_cpu" {
  alarm_name                = ""
  comparison_operator       = "GreaterThanOrEqualToThreshold"
  evaluation_periods        = 2
  metric_name               = "CPUUtilization"
  namespace                 = "AWS/AppRunner"
  period                    = 60
  statistic                 = "Average"
  threshold                 = 80
  alarm_description         = "AppRunner CPU utilization"
  insufficient_data_actions = []

dimensions = {
    ServiceName = aws_apprunner_service.main.service_name
    ServiceID   = aws_apprunner_service.main.service_id
  }
}
```

No alarms are being triggered:

![Enter image description here](/media/postImages/original/IMvovpSJ8WToaWFJ8yT9tIDA)

However it seems that data is fine:

![Enter image description here](/media/postImages/original/IMJ7bvXOETQ9m4m_CwpQYW0g)

Accepted Answer

Ok, so I discovered that after hitting some consistent requests during the defined evaluation period, data was loaded into the alarm. I can assume that this is due to the idle container features.

From the App Runner pricing page:

> When your application is idle, you pay per GB of memory for provisioned container instances which keep your application warm and eliminate cold starts. When requests come in, your application responds in milliseconds, and you pay for the vCPU and memory consumed by your active container instances as your application is processing requests.

AppRunner CloudWatch Alarm not showing metrics

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