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Create Components

In the previous steps, we've configured the repository, and decided to provision the vpc-flow-logs-bucket and vpc Terraform components into three AWS accounts (dev, staging, prod) in two AWS regions (us-east-2 and us-west-2). We've also configured the Atmos CLI to search for the components in the components/terraform directory.

We'll also put the Terraform components into the infra folder under components/terraform (note that a component can be in the components/terraform directory itself, or in any subfolder at any level in the directory).

Next step is to create the Terraform components vpc-flow-logs-bucket and vpc.

There are a few ways to create the Terraform components:

or

  • Copy the component.yaml component vendoring config file from the Atmos example components/terraform/infra/vpc-flow-logs-bucket/component.yaml into components/terraform/infra/vpc-flow-logs-bucket/component.yaml and then run the Atmos command atmos vendor pull --component infra/vpc-flow-logs-bucket from the root of the repo. The command will copy all the component's files from the open-source component repository terraform-aws-components

  • Copy the component.yaml component vendoring config file from the Atmos example components/terraform/infra/vpc/component.yaml into components/terraform/infra/vpc/component.yaml and then run the Atmos command atmos vendor pull --component infra/vpc from the root of the repo. The command will copy all the component's files from the open-source component repository terraform-aws-components

The filesystem layout should look like this:


   │  
   │   # Centralized stacks configuration
   ├── stacks
   │   └── <stack_1>
   │   └── <stack_2>
   │   └── <stack_3>
   │  
   │   # Centralized components configuration. Components are broken down by tool
   ├── components
   │   └── terraform   # Terraform components (Terraform root modules)
   │       ├── infra
   │       │   ├── vpc
   │       │   │   ├── component.yaml
   │       │   │   ├── context.tf
   │       │   │   ├── main.tf
   │       │   │   ├── outputs.tf
   │       │   │   ├── providers.tf
   │       │   │   ├── remote-state.tf
   │       │   │   ├── variables.tf
   │       │   │   ├── versions.tf
   │       │   │   ├── vpc-flow-logs.tf
   │       │   ├── vpc-flow-logs-bucket
   │       │   │   ├── component.yaml
   │       │   │   ├── context.tf
   │       │   │   ├── main.tf
   │       │   │   ├── outputs.tf
   │       │   │   ├── providers.tf
   │       │   │   ├── variables.tf
   │       │   │   ├── versions.tf

Each component follows the Standard Module Structure that Terraform recommends. There are a few additions:

  • context.tf - this file contains all the common variables that Terraform modules and components consume (to make the component's variables.tf file DRY). This is a standard file that is copied into each component. The file also defines the context variables (namespace, tenant, environment, stage) which are used by Atmos to search for Atmos stacks when executing the CLI commands

  • remote-state.tf in the vpc component - this file configures the remote-state Terraform module to obtain the remote state for the vpc-flow-logs-bucket component. The vpc Terraform component needs the outputs from the vpc-flow-logs-bucket Terraform component to configure VPC Flow Logs and store them in the S3 bucket

components/terraform/infra/vpc/remote-state.tf
module "vpc_flow_logs_bucket" {
  count = var.vpc_flow_logs_enabled ? 1 : 0

  source  = "cloudposse/stack-config/yaml//modules/remote-state"
  version = "1.3.1"

  # Specify the Atmos component name (defined in YAML stack config files) 
  # for which to get the remote state outputs
  component = var.vpc_flow_logs_bucket_component_name

  # Override the context variables to point to a different Atmos stack if the 
  # `vpc-flow-logs-bucket-1` Atmos component is provisioned in another AWS account, OU or region
  stage       = try(coalesce(var.vpc_flow_logs_bucket_stage_name, module.this.stage), null)
  tenant      = try(coalesce(var.vpc_flow_logs_bucket_tenant_name, module.this.tenant), null)
  environment = try(coalesce(var.vpc_flow_logs_bucket_environment_name, module.this.environment), null)

  # `context` input is a way to provide the information about the stack (using the context
  # variables `namespace`, `tenant`, `environment`, `stage` defined in the stack config)
  context = module.this.context
}

For a complete description of how Atmos components use remote state, refer to Component Remote State.