Let's try: Terraform part 7 - Locals, Data, and Output
These Terraform blocks can improve readability of our configurations.
In Terraform, we may have a situation to blend variables for example I want to put prefixes in BigQuery table names and comply project id as a suffix in every bucket names. Here we can use these blocks to make the configurations better with readability and flexible.
locals
locals1 is an expression to define local variables. Even though we don’t have to use locals because we can define all variables in “tfvars” files but it’s useful in some advance expressions and reusability in the same file.
Syntax
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locals {
variable_1 = "value 1"
variable_2 = "value 2"
}
resource "resource_type" "resource_name" {
attribute_1 = local.variable_1
attribute_2 = local.variable_2
}
When we declare locals block, we can refer to any variables in it by local.variable_name.
Example
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variable "new_bucket_name" {
type = string
default = "bluebirz-test-bucket-part7"
}
locals {
new_bucket_name = "${var.new_bucket_name}-new"
existing_bucket_name = "bluebirz-beam"
}
resource "google_storage_bucket" "new_bucket" {
name = local.new_bucket_name
location = "europe-west1"
}
As above, after I declared locals for 2 bucket names, one is a concatenated string (with variable reference as ${...}) and another is a plain string, I referred the first one in the resource block as name = locals.new_bucket_name.
data
data2 blocks are for querying values from existing resources but out of the Terraform configuration. It is useful in the case we want to grab some values to be references somewhere in our configs.
Syntax
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data "data_source_type" "data_source_name" {
attribute_1 = "value 1"
attribute_2 = "value 2"
}
Example
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data "google_storage_bucket" "existing_bucket" {
name = local.existing_bucket_name
}
data "google_project" "gcp_project" {
}
After terraform apply, this data.google_storage_bucket.existing_bucket will have all attribute of the existing bucket bluebirz-beam. Then we can make some uses of it later.
In case we need the current GCP project information, we can use data block for google_project.
We can find the reference of data source block of Google Cloud Storage bucket here and data source block of Google project here as well.
output
We can use output3 blocks to display particular attributes that we run terraform apply. It is much useful for reporting information of the updated infrastructure at the end of terraform apply.
Syntax
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output "output_name" {
value = resource_type.resource_name.attribute
}
Example
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output "existing_bucket_id" {
value = data.google_storage_bucket.existing_bucket.id
}
output "new_bucket_id" {
value = google_storage_bucket.new_bucket.id
}
output "gcp_project_id" {
value = data.google_project.gcp_project.project_id
}
There are 3 output blocks. First is the id of existing bucket we queried from a data block. Second is the bucket id we just created in resource block. And last one is the project id.
After terraform apply, we can see the outputs like this.
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Outputs:
existing_bucket_id = "bluebirz-beam"
gcp_project_id = "bluebirz-playground"
new_bucket_id = "bluebirz-test-bucket-part7-new"