Developing Stacks

Scope: This skill is specific to the acme infrastructure repository. It documents the stack structure, naming conventions, and deployment patterns used here. For generic component development, see developing-components.

Guide for configuring Atmos stacks to deploy Terraform components across environments.

Stack Architecture Overview

This repository uses a multi-tenant, multi-stage stack structure:

stacks/
├── orgs/acme/                         # Organization root (namespace: acme)
│   ├── _defaults.yaml                # Org-wide defaults (namespace, backend, account_map)
│   ├── core/                         # Core tenant (shared infrastructure)
│   │   ├── _defaults.yaml            # Tenant defaults (tenant: core)
│   │   ├── root/                     # Root account stage
│   │   │   ├── _defaults.yaml        # Stage defaults + auth identity
│   │   │   └── global-region/        # Global region (us-east-1)
│   │   │       └── foundation.yaml
│   │   ├── auto/                     # Automation account
│   │   ├── artifacts/                # Artifacts account (ECR, S3)
│   │   ├── audit/                    # Audit/logging account
│   │   ├── dns/                      # DNS account
│   │   ├── network/                  # Network account (TGW, VPN)
│   │   └── security/                 # Security account
│   └── plat/                         # Platform tenant (workloads)
│       ├── _defaults.yaml            # Tenant defaults (tenant: plat)
│       ├── dev/                      # Dev stage
│       │   ├── _defaults.yaml        # Stage defaults + auth identity
│       │   ├── global-region/        # Global resources (IAM)
│       │   │   └── foundation.yaml
│       │   └── us-east-1/              # Primary region
│       │       ├── foundation.yaml   # VPC, networking
│       │       ├── platform.yaml     # ECS/EKS, databases
│       │       └── app.yaml          # Application resources
│       ├── staging/                  # Staging stage
│       ├── prod/                     # Production stage
│       └── sandbox/                  # Sandbox stage
├── catalog/                          # Component defaults library
│   ├── vpc/defaults.yaml
│   ├── ecs/defaults.yaml
│   ├── eks/cluster/defaults.yaml
│   └── ...
└── mixins/                           # Reusable fragments
    ├── region/us-east-1.yaml
    └── stage/dev.yaml

Stack name format: {namespace}-{tenant}-{region_short}-{stage}

Examples for this repository:

• acme-core-use1-root - Core root account in us-east-1
• acme-plat-use1-dev - Platform dev in us-east-1
• acme-plat-use1-prod - Platform prod in us-east-1

Core Patterns

1. Catalog Defaults (Recommended Starting Point)

Define component defaults in stacks/catalog/<component>/defaults.yaml. These are imported into target stacks.

# stacks/catalog/vpc/defaults.yaml
components:
  terraform:
    vpc/defaults:
      metadata:
        type: abstract # Prevents direct deployment
      vars:
        name: vpc
        availability_zones: ["a", "b", "c"]
        public_subnets_enabled: true
        nat_gateway_enabled: true
        max_subnet_count: 3

Key points:

• Use type: abstract to prevent accidental deployment of the base configuration
• Name the component with a /defaults suffix (e.g., vpc/defaults) to indicate it's a base
• Define sensible defaults that work across most environments

2. Inheriting into Target Stacks

Import the catalog and inherit from the abstract component in your target stack:

# stacks/orgs/acme/plat/dev/us-east-1/foundation.yaml
import:
  - orgs/acme/plat/dev/_defaults
  - mixins/region/us-east-1
  - catalog/vpc/defaults

components:
  terraform:
    vpc:
      metadata:
        component: vpc # Points to components/terraform/vpc
        inherits:
          - vpc/defaults # Inherits from the abstract component
      vars:
        ipv4_primary_cidr_block: 10.2.0.0/16 # Dev environment CIDR

Inheritance merging:

• vars, settings, env, backend are deep-merged
• Later values override earlier ones
• The component's own vars override inherited vars

3. Abstract Components

Abstract components (type: abstract) serve as base configurations that cannot be deployed directly.

# Abstract - cannot be deployed
vpc/defaults:
  metadata:
    type: abstract
  vars:
    nat_gateway_enabled: true

# Real - can be deployed (inherits from abstract)
vpc:
  metadata:
    component: vpc
    inherits:
      - vpc/defaults
  vars:
    ipv4_primary_cidr_block: 10.0.0.0/16

Use abstract components when:

• Creating reusable base configurations
• Defining organization-wide defaults
• Building component "archetypes" (e.g., s3-bucket/logging, s3-bucket/public)

4. Multiple Inheritance

Components can inherit from multiple bases. Order matters - later items override earlier ones.

components:
  terraform:
    my-ecs-service:
      metadata:
        component: ecs-service
        inherits:
          - ecs-service/defaults # Base defaults
          - ecs-service/web # Web-specific settings (overrides defaults)
      vars:
        service_name: my-app # Final override

5. Stack Defaults Hierarchy

The _defaults.yaml files create an inheritance chain:

# stacks/orgs/acme/_defaults.yaml (org level)
vars:
  namespace: acme
terraform:
  backend_type: s3
  backend:
    s3:
      bucket: acme-core-use1-root-tfstate
      # ...

# stacks/orgs/acme/plat/_defaults.yaml (tenant level)
import:
  - orgs/acme/_defaults
vars:
  tenant: plat

# stacks/orgs/acme/plat/dev/_defaults.yaml (stage level)
import:
  - orgs/acme/plat/_defaults
  - mixins/stage/dev
auth:
  identities:
    plat-dev/terraform:
      default: true

Deploying a Component

Step 1: Check if Catalog Defaults Exist

ls stacks/catalog/<component>/

If defaults exist, skip to Step 3.

Step 2: Create Catalog Defaults (if needed)

# stacks/catalog/<component>/defaults.yaml
components:
  terraform:
    <component>/defaults:
      metadata:
        type: abstract
      vars:
        enabled: true
        # Add sensible defaults

Step 3: Add to Target Stack

Edit the appropriate stack file (foundation.yaml, platform.yaml, app.yaml, etc.):

import:
  # ... existing imports
  - catalog/<component>/defaults # Add this

components:
  terraform:
    <component>:
      metadata:
        component: <component>
        inherits:
          - <component>/defaults
      vars:
        # Environment-specific overrides only

Step 4: Validate and Plan

# Validate the stack configuration
atmos validate stacks

# See the resolved configuration (example for dev)
atmos describe component <component> -s acme-plat-use1-dev

# Plan the deployment
atmos terraform plan <component> -s acme-plat-use1-dev

Stack File Organization

Stack files are organized by layer:

Common Patterns

Catalog Organization for Multiple Purposes

When deploying multiple instances of the same component for different purposes, organize the catalog with abstract defaults and purpose-specific files that inherit from them:

stacks/catalog/
└── <component>/
    ├── defaults.yaml    # Abstract base component (not deployed directly)
    └── <purpose>.yaml   # Purpose-specific configuration

Abstract defaults file (stacks/catalog/<component>/defaults.yaml):

components:
  terraform:
    <component>/defaults:
      metadata:
        type: abstract # Not deployed directly
        component: <component> # Points to Terraform component
      vars:
        enabled: true
        # Organization-wide defaults for this component

Purpose-specific catalog file (stacks/catalog/<component>/<purpose>.yaml):

import:
  - catalog/<component>/defaults

components:
  terraform:
    <component>/<purpose>:
      metadata:
        component: <component> # Points to Terraform component
        inherits:
          - <component>/defaults # Inherits from abstract component
      vars:
        # Only include values that differ from defaults (keep it DRY)
        name: <purpose>-specific-name
        some_setting: override-value # Overrides default

Import in target stack:

import:
  - catalog/<component>/<purpose>

Deploy:

atmos terraform plan <component>/<purpose> -s acme-plat-use1-dev

Environment-Specific CIDR Blocks

# stacks/catalog/vpc/defaults.yaml
components:
  terraform:
    vpc/defaults:
      metadata:
        type: abstract
      vars:
        # No CIDR here - must be specified per environment

# stacks/orgs/acme/plat/dev/us-east-1/foundation.yaml
components:
  terraform:
    vpc:
      metadata:
        inherits: [vpc/defaults]
      vars:
        ipv4_primary_cidr_block: 10.2.0.0/16

# stacks/orgs/acme/plat/prod/us-east-1/foundation.yaml
components:
  terraform:
    vpc:
      metadata:
        inherits: [vpc/defaults]
      vars:
        ipv4_primary_cidr_block: 10.0.0.0/16

Cross-Component Dependencies

Use !terraform.state to wire outputs between components:

# stacks/catalog/ecs/defaults.yaml
components:
  terraform:
    ecs/defaults:
      metadata:
        type: abstract
      vars:
        vpc_id: !terraform.state vpc vpc_id
        subnet_ids: !terraform.state vpc private_subnet_ids

See the atmos-functions skill for more details.

Multiple Instances of a Component

Deploy multiple instances by using different component names:

components:
  terraform:
    # Primary VPC
    vpc:
      metadata:
        component: vpc
        inherits: [vpc/defaults]
      vars:
        ipv4_primary_cidr_block: 10.0.0.0/16

    # Secondary VPC for isolation
    vpc/isolated:
      metadata:
        component: vpc
        inherits: [vpc/defaults]
      vars:
        name: vpc-isolated
        ipv4_primary_cidr_block: 10.100.0.0/16

Debugging Stack Configuration

# See fully resolved configuration
atmos describe component <component> -s acme-plat-use1-dev

# See all components in a stack
atmos describe stacks -s acme-plat-use1-dev

# Validate all stacks
atmos validate stacks

For more debugging techniques, see the debugging-atmos skill.

References

• Atmos Design Patterns
• Component Catalog Pattern
• Stack Inheritance