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Terraform Providers

Terraform utilizes plugins known as providers for communication with cloud providers, SaaS providers, and various APIs.

In order for Terraform to install these providers, the corresponding Terraform configurations need to explicitly state what providers are required. Furthermore, certain providers require additional configuration, such as specifying endpoint URLs or cloud regions, before they can be used.

Provider Configuration in Terraform

When working with Terraform, you specify provider configurations in your Terraform code. This involves declaring which providers your infrastructure requires and providing any necessary configuration parameters. These parameters may include endpoint URLs, cloud regions, access credentials, or any other provider-specific configuration parameters.

To declare a provider in Terraform, use a provider block within your Terraform configuration files, usually in a providers.tf file in the component (a.k.a. root module) directory. The provider block specifies the provider type and all the necessary configuration parameters.

Here's an AWS provider configuration example for a vpc component. The provider config is defined in the components/terraform/vpc/providers.tf file:

components/terraform/vpc/providers.tf

  provider "aws" {
region = "us-east-2"
assume_role {
role_arn: "IAM Role ARN"
}
}

In this example, the aws provider block includes the region and IAM role required for Terraform to communicate with the AWS services.

By correctly defining provider configurations in your Terraform code, you ensure that Terraform can seamlessly install, configure, and use the necessary plugins to manage your infrastructure across various cloud and services.

Provider Configuration and Overrides in Atmos Manifests

Atmos allows you to define and override provider configurations using the providers section in Atmos stack manifests. The section can be defined globally for the entire organization, OU/tenant, account, region, or per component.

For example, the providers section at the global scope can look like this:

stacks/orgs/acme/_defaults.yaml

terraform:
providers:
aws:
region: "us-east-2"
assume_role:
role_arn: "IAM Role ARN"

Similarly, it can be defined (or overridden) at the OU/tenant, account and region scopes in the corresponding _defaults.yaml stack manifests.

If you want to override a provider configuration for a specific component, use the component.terraform.<component>.providers section. For example, the following config can be used to override the assume_role parameter just for the vpc component:

stacks/catalog/vpc/defaults.yaml

components:
terraform:
vpc:
providers:
aws:
assume_role:
role_arn: "IAM Role ARN for VPC"

You can include the providers sections in any Atmos stack manifest at any level of inheritance. Atmos will process, deep-merge and override all the providers configurations for a component in the following order:

  • Global scopes (terraform.providers sections for the Org, OUs, accounts and regions)
  • Base component scope (component.terraform.<base_component>.providers section)
  • Current component scope (component.terraform.<component>.providers section)

tip

Refer to Atmos Component Inheritance for more information on all types of component inheritance supported by Atmos


When you define the providers sections, Atmos processes the inheritance chain for a component and generates a file providers_override.tf.json in the component's folder with the final values for all the defined providers.

For example:

atmos terraform plan vpc -s plat-ue2-prod --logs-level=Trace

> atmos terraform plan vpc -s plat-ue2-prod --logs-level=Trace

Variables for the component 'vpc' in the stack 'plat-ue2-prod':
environment: ue2
max_subnet_count: 3
name: common
namespace: cp
region: us-east-2
stage: prod
tenant: plat

Writing the variables to file:
components/terraform/vpc/plat-ue2-prod.terraform.tfvars.json

Writing the provider overrides to file:
components/terraform/vpc/providers_override.tf.json

The generated providers_override.tf.json file would look like this:

providers_override.tf.json

{
"provider": {
"aws": {
"assume_role": {
"role_arn": "IAM Role ARN for VPC"
}
}
}
}

Terraform then uses the values in the generated providers_override.tf.json to override the parameters for all the providers in the file.

alias: Multiple Provider Configuration in Atmos Manifests

Atmos allows you to define multiple configurations for the same provider using a list of provider blocks and the alias meta-argument.

The generated providers_override.tf.json file will have a list of provider configurations, and Terraform/OpenTofu will use and override the providers as long as the aliased providers are defined in the Terraform component.

For example:

stacks/catalog/vpc/defaults.yaml

components:
terraform:
vpc:
providers:
aws:
- region: us-west-2
assume_role:
role_arn: "role-1"
- region: us-west-2
alias: "account-2"
assume_role:
role_arn: "role-2"

warning

The above example uses a list of configuration blocks for the aws provider.

Since it's a list, by default it doesn't work with deep-merging of stacks in the inheritance chain since list are not deep-merged, they are replaced.

If you want to use the above configuration in the inheritance chain and allow appending or merging of lists, consider configuring the settings.list_merge_strategy in the atmos.yaml CLI config file.

For more details, refer to Atmos CLI Settings.


References