getting terraform reference for AWS CloudWatch alarm

Question

The following terraform resource creates AWS cloudwatch alarm, but remains in "insufficient data" state. I believe this is due to some of the dimension names I used (DevicePath, fstype) may not be correct. I know the names MountPath and InstanceID are correct but could not verify the other two (DevicePath, fstype). AWS call these dimensions as path, device, fstype and host respectively, however, could not find a reference what terraform calls these.

resource "aws_cloudwatch_metric_alarm" "Low_Disk_Space_For_root_drive" {
  alarm_name                = "Low_Disk_Space_For_root_drive"
  comparison_operator       = "GreaterThanOrEqualToThreshold"
  evaluation_periods        = "2"
  metric_name               = "disk_used_percent"
  namespace                 = "CWAgent"

  dimensions {
    MountPath = "/"
    DevicePath = "/dev/xvda2"
    fstype = "xfs"
    InstanceId = "i-xxxxxxxxxxxxxxxxx"

  }

  period                    = "60"
  statistics                = "Maximum"
  threshold                 = "90" 
  alarm_description         = "Disk usage for / is high"
  insufficient_data_actions = []
  actions_enabled           = true
  alarm_actions             = ["arn:aws:sns:xxxxxx"]
  ok_actions                = ["arn:aws:sns:xxxxxx"]
}

Answer 1

Add TreatMissingData to resource body

resource "aws_cloudwatch_metric_alarm" "Low_Disk_Space_For_root_drive"{
  alarm_name                = "Low_Disk_Space_For_root_drive"
 comparison_operator       = "GreaterThanOrEqualToThreshold"
 evaluation_periods        = "2"
 metric_name               = "disk_used_percent"
 namespace                 = "CWAgent"

 dimensions {
   MountPath = "/"
   DevicePath = "/dev/xvda2"
   fstype = "xfs"
   InstanceId = "i-xxxxxxxxxxxxxxxxx"

  }

  period                    = "60"
  statistics                = "Maximum"
  threshold                 = "90" 
  alarm_description         = "Disk usage for / is high"
  insufficient_data_actions = []
  **TreatMissingData = "notBreaching"**
  actions_enabled           = true
  alarm_actions             = ["arn:aws:sns:xxxxxx"]
  ok_actions                = ["arn:aws:sns:xxxxxx"]
}

Answer 2

In order to make this work you need to

• Change MountPath to path
• Remove DevicePath and instead add device
• Add ImageID and InstanceType

Check out the updated dimensions field below

(Note - substitute the values with your own values. You should be able to see them from the Cloudwatch Metrics CWAgent section on the AWS console)

resource "aws_cloudwatch_metric_alarm" "Low_Disk_Space_For_root_drive" {
  alarm_name                = "Low_Disk_Space_For_root_drive"
  comparison_operator       = "GreaterThanOrEqualToThreshold"
  evaluation_periods        = "2"
  metric_name               = "disk_used_percent"
  namespace                 = "CWAgent"

  dimensions {
      InstanceId    = "i-xxxxxxxxxxxxxxxxx"
      ImageId       = "your-image-id"
      InstanceType  = "your-instance-type"
      path          = "/"
      device        = "your-device"
      fstype        = "xfs"

  }

  period                    = "60"
  statistics                = "Maximum"
  threshold                 = "90" 
  alarm_description         = "Disk usage for / is high"
  insufficient_data_actions = []
  actions_enabled           = true
  alarm_actions             = ["arn:aws:sns:xxxxxx"]
  ok_actions                = ["arn:aws:sns:xxxxxx"]
}

Answer 3

Main reason why is because what you put as device

Change "/dev/xvda2" to AWS the exact device like ("nvme1n1"). You can check that in CloudWatch Metrics.