By Sebastian Stadil —

IaC Stack Evaluation Criteria

Infrastructure as Code (IaC) with tools like Terraform and its open-source alternative, OpenTofu, has become standard practice. They bring automation, consistency, and speed to infrastructure provisioning. However, as your usage scales, managing raw IaC configurations can introduce new complexities: code duplication, state management headaches, inconsistent governance, and collaboration bottlenecks. This post aims to help you evaluate different approaches to address these challenges by focusing on key decision-making criteria.

Platform engineering teams are increasingly looking beyond vanilla IaC, exploring a rich ecosystem of tools to regain control and efficiency. Let's look at common approaches through the lens of evaluation criteria.

Key Evaluation Criteria for Your IaC Stack

Before diving into solutions, it's crucial to establish the criteria against which you'll evaluate them. These typically stem from the common pain points experienced at scale:

  • DRY (Don't Repeat Yourself) Principle / Code Reusability: How well does the solution help in avoiding repetitive code for backend configurations, provider settings, or similar environments?
  • State Management Effectiveness: How effectively and securely does the solution manage state files? Does it prevent performance bottlenecks and minimize the blast radius of potential issues?
  • Environment & Workspace Management: How capable is the solution in handling distinct configurations for dev, staging, and prod across different teams or accounts without introducing chaos?
  • Governance & Policy Enforcement: What capabilities does the solution offer for enforcing security best practices, compliance standards, and consistent tagging?
  • Collaboration & Workflow Automation: How does the solution streamline team reviews, approvals, and the application of infrastructure changes? Does it integrate well with GitOps workflows?
  • Cost Visibility & Management: Does the solution provide insights into the cost implications of infrastructure changes before they are applied, and does it help manage ongoing costs?
  • Operational Overhead & Maintainability: What is the learning curve, setup effort, and ongoing maintenance burden associated with the solution?
  • Scalability & Flexibility: Can the solution scale with your organization's needs and adapt to different workflow preferences?

Evaluating IaC Tooling Options Against Key Criteria

With these criteria in mind, let's examine various tooling options.

1. Terragrunt: Excelling in DRY Configurations and State Management Automation

When your primary evaluation criteria include achieving DRY configurations and simplified remote state management, Terragrunt offers significant advantages. It acts as a thin wrapper around Terraform/OpenTofu, primarily focused on reducing code duplication and simplifying remote state configuration. It allows you to define common configurations once and inherit them.

Example: Terragrunt terragrunt.hcl for DRY Backend Configuration This example demonstrates how Terragrunt helps centralize backend configuration, a key aspect of the DRY principle and effective state management.

// terragrunt.hcl (in a parent directory)
remote_state {
  backend = "s3"
  config = {
    bucket         = "my-terraform-states-central"
    key            = "path/to/my/project/${path_relative_to_include()}/terraform.tfstate"
    region         = "us-east-1"
    encrypt        = true
    dynamodb_table = "terraform-locks"
  }
  generate = {
    path      = "backend.tf"
    if_exists = "overwrite_terragrunt"
  }
}

inputs = {
  common_tag = "my-app"
}

Child modules would then simply include this, inheriting the backend setup and common inputs, directly addressing the DRY and state management criteria.

2. Atmos: Meeting Criteria for Orchestration and Hierarchical Configuration

If your evaluation criteria emphasize comprehensive orchestration of components, hierarchical YAML-based configuration, and potentially tool-agnostic capabilities, Atmos presents a compelling option. It takes a higher-level approach, using YAML to define "stacks" that orchestrate various "components" (often Terraform modules).

Example: Conceptual Atmos Stack Snippet This snippet illustrates how Atmos defines and orchestrates components, aligning with criteria for structured environment management and component orchestration.

# stacks/ue1-prod.yaml
import:
  - org/platforn/defaults # Inherits base configurations
  - catalog/vpc           # Imports a VPC component definition
  - catalog/eks           # Imports an EKS component definition

vars: # Environment-specific variables
  environment: prod
  region: us-east-1

components:
  terraform: # Specifies components to be managed by Terraform
    vpc:
      vars: # Component-specific variables
        instance_tenancy: dedicated
    eks:
      vars:
        node_count: 5

Atmos allows for a clear separation of concerns and promotes reusability through its stack and component model, addressing criteria related to modularity and scalable configuration management.

3. TACOS: Addressing Collaboration, Governance, and Managed Operations Criteria

For organizations where evaluation criteria heavily weigh on secure remote state management, GitOps integration, Policy-as-Code (PaC), Role-Based Access Control (RBAC), cost estimation/visibility, and enhanced collaboration features, Terraform Automation and Collaboration Software (TACOS) platforms provide a managed solution. These platforms (e.g., Terraform Cloud, Spacelift, Env0, and Scalr) offer a service layer for your IaC workflows.

Platforms like Scalr particularly shine when evaluated against criteria such as structured, hierarchical environment management (Account > Environment > Workspace) and flexible workflow options. This allows central platform teams to set global standards (credentials, OPA policies, module registries) while empowering development teams with self-service capabilities within their isolated, permissioned environments. This approach aligns well with organizations aiming to centralize administration but decentralize operations effectively. Furthermore, robust OpenTofu support makes such platforms adaptable to diverse team needs and future-proof, fulfilling the scalability and flexibility criterion.

Example: Atlantis-style PR Comment for GitOps This demonstrates a common TACOS workflow, directly addressing the collaboration and workflow automation criterion by integrating IaC operations into the PR process.

# In a GitHub Pull Request comment
atlantis plan -d my-infra-module/

This would trigger a plan and post the output back to the PR for review, enhancing transparency and control.

4. DIY: Prioritizing Customization and Control

Evaluating the DIY path involves weighing the criterion of maximum customization and control against criteria like development overhead, ongoing maintenance, and operational complexity. Some organizations, especially those with mature platform teams, build custom tooling. This can range from wrapper scripts to full-fledged internal developer portals. While offering a perfectly tailored fit, this path comes with significant development and maintenance responsibilities.

Comparative Evaluation: Matching Tools to Your Priorities

The right approach depends on how your organization prioritizes these evaluation criteria based on its size, complexity, and maturity. The table below summarizes how different approaches generally perform against key criteria:

Evaluation Criterion

Vanilla TF/OpenTofu

Terragrunt

Atmos

TACOS (e.g., Scalr)

DIY

DRY Configurations

Fair (Modules)

Excellent (HCL)

Excellent (YAML)

Good (Module Registries, Templates)

Variable

State Management

Manual Setup

Good (Automates Backend)

Good (Orchestrates Backend)

Excellent (Managed, Secure, Locking)

Custom Build

Env. Management

Workspaces (Limited)

Excellent (Hierarchy)

Excellent (Stacks)

Excellent (Hierarchical Scopes, RBAC, Workspaces)

Variable

Governance (PaC)

Poor

Via External Tools

Good (OPA for Stacks)

Excellent (OPA/Sentinel, RBAC)

Custom Integration

Collaboration/Workflow

Basic (VCS)

Improves Structure

Improves Structure

Excellent (PR Flows, UI, Approvals)

Custom CI/CD

Cost Estimation/Visibility

None

Via External Tools

Via External Tools

Good to Excellent (Integrated or via integrations)

Custom Integration

Workflow Flexibility

CLI Only

CLI (Wraps TF)

CLI (Orchestrates Tools)

Excellent (CLI, GitOps, No-Code, API)

As Designed

Operational Overhead

Low (Tool itself)

Medium (Learning Curve, Setup)

Medium-High (Broader Scope)

Low (SaaS) / Medium (Self-hosted components)

Very High (Dev & Maintenance)

Conclusion: Choosing Based on Your Evaluation

Scaling IaC effectively means moving beyond basic commands and thoughtfully evaluating tools against your specific needs. Tools like Terragrunt and Atmos offer powerful ways to structure and orchestrate your code, excelling against criteria of code reusability and organized management. For comprehensive management, governance, and collaboration—key criteria for many scaling organizations—TACOS platforms provide compelling solutions. Many, like Scalr, are designed to help platform teams offer infrastructure as a secure, self-service product, supporting both Terraform and OpenTofu.

Ultimately, the key is to clearly define your evaluation criteria, understand the trade-offs of each approach, and choose a strategy that reduces friction and empowers your teams to deliver value, rather than wrestle with tooling.