Looping over local json using for-each in Terraform - terraform

Question

I am trying to create multiple cloudwatch alarms using input from a json file or json locally declared. Either is fine. I've removed the list of
The problem is that this is within a module, so I cannot use file.auto.tfvars.json which is how I previously did this.
File structure:
.
├── cloudwatch.tf
├── cloudwatchalarms.json
└── locals.tf
What I've tried so far:
Use jsondecode to bring in the cloudwatchalarms.json and loop over it in the following way:
cloudwatch.tf
# creates alarms based on what exists within cloudwatchalarms.auto.tfvars.json
resource "aws_cloudwatch_metric_alarm" "alarms" {
for_each = { for alarm in local.all_alarms : alarm => alarm }
alarm_name = "${var.awsResourceName}-${each.value.Identifier}"
namespace = each.value.Namespace
comparison_operator = each.value.ComparisonOperator
evaluation_periods = each.value.EvaluationPeriods
statistic = each.value.Statistic
treat_missing_data = each.value.TreatMissingData
threshold = each.value.Threshold
period = each.value.Period
metric_name = each.value.MetricName
dimensions = {
EcsServiceName = var.awsResourceName
EcsClusterName = var.ecs_cluster_name
}
}
locals.tf
# create locals to pull in cloudwatchalarms.json
locals {
cloudwatchAlarms = jsondecode(file("${path.module}/cloudwatchalarms.json"))
# loop over the cloudwatchalarms json structure
all_alarms = [for alarms in local.cloudwatchAlarms.cloudwatchAlarms : alarms.Identifier]
}
cloudwatchalarms.json
{
"cloudwatchAlarms": [
{
"Identifier": "ServiceMemoryUtilisation",
"Namespace": "AWS/ECS",
"MetricName": "MemoryUtilization",
"Statistic": "Average",
"Threshold": 90,
"Period": 60,
"EvaluationPeriods": 5,
"ComparisonOperator": "GreaterThanThreshold",
"TreatMissingData": "missing"
},
{
"Identifier": "ServiceCPUUtilisation",
"Namespace": "AWS/ECS",
"MetricName": "CPUUtilization",
"Statistic": "Average",
"Threshold": 90,
"Period": 60,
"EvaluationPeriods": 5,
"ComparisonOperator": "GreaterThanThreshold",
"TreatMissingData": "missing"
}
]
}
}
When using this method I get the following errors for every attribute:
Error: Unsupported attribute
on .terraform/modules/terraform-ecs-monitoring/cloudwatch.tf line 4, in resource "aws_cloudwatch_metric_alarm" "alarms":
4: alarm_name = "${var.awsResourceName}-${each.value.Identifier}"
|----------------
| each.value is "TaskStability"
This value does not have any attributes.
The second method I tried using was declaring the json structure in locals
cloudwatch.tf
# creates alarms based on what exists within cloudwatchalarms.auto.tfvars.json
resource "aws_cloudwatch_metric_alarm" "alarms" {
for_each = { for alarm in local.cloudwatchAlarms : alarm.Identifier => alarm }
alarm_name = "${var.awsResourceName}-${each.value.Identifier}"
namespace = each.value.Namespace
comparison_operator = each.value.ComparisonOperator
evaluation_periods = each.value.EvaluationPeriods
statistic = each.value.Statistic
treat_missing_data = each.value.TreatMissingData
threshold = each.value.Threshold
period = each.value.Period
metric_name = each.value.MetricName
dimensions = {
EcsServiceName = var.awsResourceName
EcsClusterName = var.ecs_cluster_name
}
}
locals.tf
locals {
cloudwatchAlarms = {
"cloudwatchAlarms": [
{
"Identifier": "ServiceMemoryUtilisation",
"Namespace": "AWS/ECS",
"MetricName": "MemoryUtilization",
"Statistic": "Average",
"Threshold": 90,
"Period": 60,
"EvaluationPeriods": 5,
"ComparisonOperator": "GreaterThanThreshold",
"TreatMissingData": "missing"
},
{
"Identifier": "ServiceCPUUtilisation",
"Namespace": "AWS/ECS",
"MetricName": "CPUUtilization",
"Statistic": "Average",
"Threshold": 90,
"Period": 60,
"EvaluationPeriods": 5,
"ComparisonOperator": "GreaterThanThreshold",
"TreatMissingData": "missing"
}
]
}
}
I then get this error when trying this method:
Error: Unsupported attribute
on .terraform/modules/terraform-ecs-monitoring/cloudwatch.tf line 3, in resource "aws_cloudwatch_metric_alarm" "alarms":
3: for_each = { for alarm in local.cloudwatchAlarms : alarm.Identifier => alarm }
This value does not have any attributes.
Throw to stop pipeline
Any help or pointing in the right direction would be great. Thanks.

Answer 1

You are closer to correctly constructing the set(object) in the first attempt, and restructuring the data in the second attempt. When combining the two, we arrive at:
locals {
cloudwatchAlarms = jsondecode(file("${path.module}/cloudwatchalarms.json"))
}
resource "aws_cloudwatch_metric_alarm" "alarms" {
for_each = { for alarm in local.cloudwatchAlarms : alarm.Identifier => alarm }
...
}
and your for_each meta-argument iterates over the set(object) (implicitly converted from the tuple type) and retrieves the value for the Identifier key in each object and the entire object. Your Map constructor in the for expression assigns the former to the key and the latter to the value, which when iterated upon will give you the desired behavior for the body of your resource block as it currently exists in the question.
Note also that:
alarm_name = "${var.awsResourceName}-${each.value.Identifier}"
can be simplified to:
alarm_name = "${var.awsResourceName}-${each.key}"

Answer 2

I sorted this with the following configuration:
locals.tf
# create locals to pull in cloudwatchalarms.json
locals {
cloudwatch_alarms = jsondecode(file("${path.module}/cloudwatchalarms.json"))
# loop over the cloudwatchalarms json structure
all_alarms = { for alarms in local.cloudwatch_alarms.cloudwatchAlarms : alarms.Identifier => alarms }
}
cloudwatchalarms.json
{
"cloudwatchAlarms": [
{
"Identifier": "ServiceMemoryUtilisation",
"Namespace": "AWS/ECS",
"MetricName": "MemoryUtilization",
"Statistic": "Average",
"Threshold": 90,
"Period": 60,
"EvaluationPeriods": 5,
"ComparisonOperator": "GreaterThanThreshold",
"TreatMissingData": "missing"
},
{
"Identifier": "ServiceCPUUtilisation",
"Namespace": "AWS/ECS",
"MetricName": "CPUUtilization",
"Statistic": "Average",
"Threshold": 90,
"Period": 60,
"EvaluationPeriods": 5,
"ComparisonOperator": "GreaterThanThreshold",
"TreatMissingData": "missing"
}
]
}
}
cloudwatch.tf
# creates alarms based on what exists within cloudwatchalarms.auto.tfvars.json
resource "aws_cloudwatch_metric_alarm" "alarms" {
for_each = { for alarm in local.all_alarms : alarm.Identifier => alarm }
alarm_name = "${var.awsResourceName}-${each.value.Identifier}"
namespace = each.value.Namespace
comparison_operator = each.value.ComparisonOperator
evaluation_periods = each.value.EvaluationPeriods
statistic = each.value.Statistic
treat_missing_data = each.value.TreatMissingData
threshold = each.value.Threshold
period = each.value.Period
metric_name = each.value.MetricName
dimensions = {
EcsServiceName = var.awsResourceName
EcsClusterName = var.ecs_cluster_name
}
}
The fix was changing this line in locals.tf to the following:
all_alarms = { for alarms in local.cloudwatch_alarms.cloudwatchAlarms : alarms.Identifier => alarms }
So this is now a map.
Then in cloudwatch.tf changing the for_each to the following:
for_each = { for alarm in local.all_alarms : alarm.Identifier => alarm }