Terraform-provider-aws: Passing list into Dimension field in Cloudwatch alarm?

[hashibot]

_This issue was originally opened by @davyt10 as hashicorp/terraform#8600. It was migrated here as part of the provider split. The original body of the issue is below._

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v0.7.2
Could anyone suggest the correct syntax to pass a list of instances in the dimensions filed for a cloudwatch alarm?

resource "aws_cloudwatch_metric_alarm" "cpu_credits" {
  alarm_name = "test - Low CPU Credits"
  comparison_operator = "LessThanOrEqualToThreshold"
  #dimensions { InstanceId = "${var.instID}" }
  dimensions { InstanceId = "i-07656896d6947814c", InstanceId = "i-042e664331a74e385" }
  evaluation_periods = "10"
  metric_name = "CPUCreditBalance"
  namespace = "AWS/EC2"
  period = "120"
  statistic = "Average"
  threshold = "200"
  alarm_description = "This metric monitors low ec2 cpu credits for T2 instances"
  insufficient_data_actions = []
  alarm_actions = ["arn:aws:sns:eu-west-1:623990728151:CloudwatchAlerts"]
}

[mildwonkey]

Hi @davyt10
Sorry for the very delayed response!
AWS CloudWatch alarms are instance-specific. If you want to monitor multiple instances, you would need to create an alarm for each instance.

Here's an example that creates multiple alarms without repeated code:

```hcl

variable "instances" {
default = ["i-07656896d6947814c", "i-042e664331a74e385"]
}

resource "aws_cloudwatch_metric_alarm" "cpu_credits" {
count = "${length(var.instances)}"
## alarm names must be unique in an AWS account
alarm_name = "test-${count.index} - Low CPU Credits
comparison_operator = "LessThanOrEqualToThreshold"
#dimensions { InstanceId = "${var.instID}" }
dimensions { InstanceId = "${element(var.instances, count.index)}"
evaluation_periods = "10"
metric_name = "CPUCreditBalance"
namespace = "AWS/EC2"
period = "120"
statistic = "Average"
threshold = "200"
alarm_description = "This metric monitors low ec2 cpu credits for T2 instances"
insufficient_data_actions = []
alarm_actions = ["arn:aws:sns:eu-west-1:623990728151:CloudwatchAlerts"]
}```

[ac-hibbert]

This is useful but I am wandering how to do the same thing when you are also creating the instances with terraform? I tried locals

locals {
  instance_ids = ["${aws_instance.host1.id}", "${aws_instance.host2.id}", "${aws_instance.host3.id}"]
}

But later on when I use the count I get the following

value of 'count' cannot be computed
```

[bflad]

Closing due to lack of response from original author.

For tracking value of 'count' cannot be computed issues, I would recommend looking upstream in the Terraform core issue tracker, as count is not handled by Terraform providers themselves. See also: https://github.com/hashicorp/terraform/issues?utf8=%E2%9C%93&q=is%3Aissue+is%3Aopen+value+of+count+cannot+be+computed

[tb3088]

AWS CloudWatch alarms are instance-specific.

No, they are attribute specific. It is perfectly valid to define dimensions that use tags, or ami-id, or instance size as selection criteria. The more interesting question is whether the provider can be extended to support an array of multiple types. The typical 'hack' is to pass a comma-delimited string with no delimiting spaces but one would have to read the source to see how the code is written and whether it handles that case.

[hashibot[bot]]

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