# Configuration Overview

Atmos uses multiple types of configuration files, each serving a distinct purpose. Understanding these configuration types is essential for effectively managing your infrastructure.

## Configuration Types

Atmos organizes configuration into four main categories:

| Configuration Type | File(s) | Purpose |
|-------------------|---------|---------|
| **[CLI Configuration](#cli-configuration)** | `atmos.yaml` | Configure the Atmos CLI behavior, paths, and integrations |
| **[Stack Configuration](#stack-configuration)** | `stacks/**/*.yaml` | Define environments and component configurations |
| **[Component Configuration](#component-configuration)** | `components/` | Infrastructure code (Terraform, Helmfile, Packer) |
| **[Vendor Configuration](#vendor-configuration)** | `vendor.yaml` | Define external dependencies to vendor |

## CLI Configuration

The `atmos.yaml` file configures the Atmos CLI itself. It tells Atmos where to find your stacks and components, how to behave, and what integrations to enable.

**Key settings include:**

- Base paths for components, stacks, and workflows
- Terraform/Helmfile command configuration
- Stack naming patterns
- Template and schema settings
- Integrations (Atlantis, Spacelift, GitHub Actions)

```yaml
# atmos.yaml
base_path: "."

components:
  terraform:
    base_path: components/terraform

stacks:
  base_path: stacks
  included_paths:
    - "orgs/**/*"
  name_pattern: "{tenant}-{environment}-{stage}"
```

[Learn more about CLI Configuration →](/cli/configuration)

## Stack Configuration

Stack configuration files define your environments and how components are configured within them. Stacks are YAML files that specify which components to deploy and with what settings.

**Key features:**

- Component definitions with variables and metadata
- Imports for configuration reuse
- Inheritance between configurations
- Environment-specific overrides

```yaml
# stacks/prod/us-east-1.yaml
import:
  - catalog/vpc/defaults

components:
  terraform:
    vpc:
      vars:
        environment: ue1
        stage: prod
        cidr_block: "10.0.0.0/16"
```

[Learn more about Stack Configuration →](/stacks)

## Component Configuration

Components are the infrastructure-as-code implementations that Atmos orchestrates. Each component type has its own configuration within stacks:

### Terraform Components

Terraform root modules in `components/terraform/`. Stack configuration tells Atmos which module to use and what variables to pass.

```yaml
components:
  terraform:
    vpc:
      metadata:
        component: vpc  # Points to components/terraform/vpc/
      vars:
        cidr_block: "10.0.0.0/16"
```

[Terraform Stack Configuration →](/components/terraform/stack-config)

### Helmfile Components

Helmfile configurations in `components/helmfile/`. Used for deploying Helm charts to Kubernetes.

```yaml
components:
  helmfile:
    nginx-ingress:
      vars:
        namespace: ingress
        chart_version: "4.0.0"
```

[Helmfile Configuration →](/components/helmfile)

### Packer Components

Packer templates in `components/packer/`. Used for building machine images.

```yaml
components:
  packer:
    ubuntu-base:
      vars:
        ami_name: "ubuntu-base"
        instance_type: "t3.medium"
```

[Packer Configuration →](/components/packer)

## Vendor Configuration

Vendor manifests define external dependencies that Atmos should download and manage. This enables you to use third-party components, modules, and configurations without copying them into your repository.

```yaml
# vendor.yaml
apiVersion: atmos/v1
kind: AtmosVendorConfig
metadata:
  name: my-vendor-config
spec:
  sources:
    - component: vpc
      source: github.com/cloudposse/terraform-aws-components.git//modules/vpc
      version: 1.300.0
```

[Learn more about Vendoring →](/vendor/)

## Configuration Hierarchy

These configuration types work together in a hierarchy:

1. **CLI Configuration** (`atmos.yaml`) defines where to find everything
2. **Vendor Configuration** (`vendor.yaml`) pulls in external dependencies
3. **Component Configuration** (`components/`) provides the infrastructure code
4. **Stack Configuration** (`stacks/`) assembles components into deployable environments

```
atmos.yaml                    # CLI: Where to find things
├── vendor.yaml               # Vendor: External dependencies
├── components/               # Components: Infrastructure code
│   ├── terraform/
│   ├── helmfile/
│   └── packer/
└── stacks/                   # Stacks: Environment definitions
    ├── catalog/              # Reusable configurations
    └── orgs/                 # Environment-specific stacks
```

## Next Steps

- [CLI Configuration](/cli/configuration) — Configure Atmos behavior
- [Stack Configuration](/stacks) — Define your environments
- [Components](/stacks/components) — Configure components in stacks
- [Vendoring](/vendor/) — Manage external dependencies