In terraform, how to loop over a list of objects and update values? - terraform

Question

I will be providing values with terragrunt. The variable, push_subscriptions, is a list of maps and I want to modify the values of the map. For example, append a prefix to the push subscription name in place like so (within the main.tf):
push_subscriptions[index]['name'] = "$pbsb-push-${var.product_environment_code}-push_subscriptions[index]['name']"
main.tf
module "pubsub" {
push_subscriptions = var.push_subscriptions
}
terragrunt.hcl
include "product_vars" {
path = find_in_parent_folders("_terragrunt.hcl")
}
inputs = {
push_subscriptions = [
{
name = "push-sub-1"
ack_deadline_seconds = 20
push_endpoint = "https://example.com"
},
{
name = "push-sub-2"
ack_deadline_seconds = 20
push_endpoint = "https://example.com"
}
]
}

Answer 1

Shouldn't be a problem. Just create a local where you'll be using it, that iterates over the list and returns another list of objects with the updated values.
In this example, local.subs is used in lieu of your variable, but you would just replace local.subs with var.push_subscriptions in your case.
locals {
subs = [
{ name = "foo" },
{ name = "bar" },
]
updated = [for sub in local.subs : { name = "some-prefix-${sub.name}" }]
}
output "updated" {
value = local.updated
}
Which gives:
Changes to Outputs:
+ updated = [
+ {
+ name = "some-prefix-foo"
},
+ {
+ name = "some-prefix-bar"
},
]
So that is a new value you can use with prefixes.
Or you could do this entirely in line, with something like:
module "pubsub" {
push_subscriptions = [for sub in var.push_subscriptions : merge(sub, {
name = "pbsb-push-${var.product_environment_code}-some-prefix-${sub.name}"
})]
}
Using merge here allows you to maintain all the other values.