Atlantis for Cost Optimization

Table of Contents

1. The Power of IaC Automation in Controlling Cloud Spend
2. Shifting Cost Awareness Left: Pre-Apply Cost Checks
3. Practical Use Cases for Driving Significant Cost Savings
4. The Importance of Tracking and Tagging for Financial Visibility
5. Advanced Cost Control: Custom Workflows and API Integration
6. Beyond Self-Managed: When Platforms Like Scalr Make Sense
7. Summary: Key Approaches to IaC-Driven Cost Optimization
8. Conclusion: Embedding Cost Consciousness into Your Operations

1. The Power of IaC Automation in Controlling Cloud Spend

At its core, IaC brings discipline. By defining infrastructure in code, organizations gain version control, repeatability, and a clear audit trail. Automation tools like Atlantis build on this by integrating IaC practices directly into pull request (PR) workflows.

• Preventing Unnecessary Provisioning: Every proposed infrastructure change (a new server, a modified database setting) is visible within a PR. Atlantis automatically runs terraform plan, showing exactly what will be created, modified, or destroyed. This transparency, coupled with mandatory peer reviews, acts as a critical checkpoint, preventing accidental or unjustified resource deployment that can lead to cost blowouts.
• Effective Resource Lifecycle Management: IaC excels at defining the entire lifecycle of resources. Temporary development or testing environments can be spun up and, crucially, torn down systematically when no longer needed. This prevents the accumulation of "zombie" infrastructure – resources that are forgotten but continue to incur charges.

This systematic approach, enforced by an automation layer, is fundamental to preemptive cost control.

2. Shifting Cost Awareness Left: Pre-Apply Cost Checks

One of the most effective ways to control costs is to make them visible before deployment. Integrating cost estimation tools like Infracost into the Atlantis PR workflow is a game-changer.

When a developer submits a PR with Terraform changes, Infracost can analyze the plan and post a comment detailing the estimated cost impact. This "shifts left" cost awareness, empowering engineers to make more cost-conscious decisions.

Setting up Infracost with Atlantis:

This typically involves using a custom Atlantis Docker image that includes Infracost or configuring workflow hooks. An atlantis.yaml or server-side repos.yaml might look like this:

# Example atlantis.yaml for Infracost integration
workflows:
  terraform-infracost:
    plan:
      steps:
        - init
        - plan # Generates $PLANFILE
        - show # Generates $SHOWFILE (JSON plan)
        - run: |
            infracost breakdown --path $SHOWFILE \
                              --format json \
                              --out-file "/tmp/infracost-$BASE_REPO_OWNER-$BASE_REPO_NAME-$PULL_NUM-$WORKSPACE.json"
    apply:
      steps:
        - apply
repos:
  - id: /.*/
    workflow: terraform-infracost
    post_workflow_hooks:
      - run: |
          # Ensure GITHUB_TOKEN and INFRACOST_API_KEY are set
          infracost comment github --path "/tmp/infracost-$BASE_REPO_OWNER-$BASE_REPO_NAME-$PULL_NUM-*.json" \
                                 --repo $BASE_REPO_OWNER/$BASE_REPO_NAME \
                                 --pull-request $PULL_NUM \
                                 --github-token $GITHUB_TOKEN \
                                 --behavior update
        commands: plan

This setup provides valuable cost insights directly in the PR. However, managing custom Docker images, API keys, and complex workflow configurations can add operational overhead. Platforms like Scalr often aim to simplify such integrations, potentially offering native cost estimation features or more streamlined connections to tools like Infracost, reducing the setup burden and providing a more cohesive experience.

3. Practical Use Cases for Driving Significant Cost Savings

With an Atlantis-driven workflow, several key cost-saving strategies become more manageable:

3.1. Identifying and Axing Unused Resources

The PR process for decommissioning ensures that removing resources is as deliberate as creating them. When Terraform code for a service is removed, the terraform plan in the PR clearly shows what will be destroyed, allowing for verification before atlantis apply executes the changes. This helps eliminate orphaned resources that quietly drain budgets.

3.2. Rightsizing: Paying Only for What You Need

Overprovisioning is rampant. Rightsizing involves adjusting resources (e.g., VM sizes, database capacity) to match actual demand.

1. Monitoring tools identify an underutilized resource.
2. A developer creates a PR to change the instance type in Terraform.
3. Atlantis runs plan; Infracost (if integrated) shows the cost savings.
4. Reviewers approve, and atlantis apply implements the change.

This systematic review of sizing changes, backed by cost estimates, ensures that optimizations are deliberate and impactful.

3.3. Automating Non-Production Environment Lifecycles

Dev, test, and staging environments often don't need to run 24/7. Terraform can define their "shutdown" state (e.g., scaling ASGs to zero). The Atlantis API can then be called by external schedulers (cron, Lambda) to apply these configurations during off-hours and restart them when needed, leading to substantial savings. While Atlantis provides the API, managing the scheduling and state logic still falls on the user. Scalr, in contrast, often includes more built-in concepts for environment management and scheduling, potentially simplifying these common cost-saving patterns.

4. The Importance of Tracking and Tagging for Financial Visibility

Understanding the cost impact of changes and allocating costs correctly requires diligent tracking and tagging.

• PR History as an Audit Trail: The combination of Git history and Atlantis PR logs (plans, applies, approvals) provides a rich audit trail for infrastructure modifications. This can be correlated with billing data to understand cost fluctuations.
• Robust Resource Tagging: Tags are crucial for categorizing resources in cloud billing reports. Terraform is used to define these tags, and Atlantis ensures they are applied.

Enforcing Tagging Policies:

Consistent tagging is key. Terraform's default_tags feature (in providers like AWS) helps establish a baseline:

# Example AWS provider default_tags
provider "aws" {
  region = "us-east-1"
  default_tags {
    tags = {
      Environment = var.environment
      Project     = "phoenix"
      CostCenter  = "engineering-123"
      ManagedBy   = "Terraform-Atlantis"
    }
  }
}

For more advanced enforcement, policy-as-code tools like Open Policy Agent (OPA) with Conftest can be integrated into Atlantis workflows using pre_workflow_hooks. A Rego policy might check for mandatory tags:

package main

minimum_required_tags := {"Environment", "Project", "Owner", "CostCenter"}

deny[msg] {
  resource := input.resource_changes[_].change.after
  provided_tags := {key | resource.tags[key]}
  missing_tags := minimum_required_tags - provided_tags
  count(missing_tags) > 0
  msg := sprintf("Resource '%s' is missing required tags: %v", [input.resource_changes[_].address, missing_tags])
}

If conftest test <plan_output.json> fails due to policy violations, the Atlantis workflow can be halted.

While these methods offer powerful control, implementing and managing comprehensive tagging and policy enforcement across many repositories and teams with a self-managed tool like Atlantis can become complex. Centralized IaC platforms like Scalr often provide more sophisticated, built-in policy engines and hierarchical tagging strategies, simplifying governance and ensuring consistency at scale.

5. Advanced Cost Control: Custom Workflows and API Integration

Atlantis's flexibility allows for more tailored cost control:

• Targeted Operations: Commands like atlantis plan -p project-alpha -- -destroy allow precise actions on specific projects or workspaces, useful for decommissioning specific environments.
• API for Automation: The Atlantis API (/api/plan, /api/apply) enables external systems to trigger Terraform runs, facilitating scheduled cleanups or event-driven scaling.
• Workflow Hooks: pre_workflow_hooks can run custom scripts for budget adherence checks or advanced policy validation before a plan or apply. post_workflow_hooks can notify financial dashboards or trigger secondary automation after changes are made.

These features allow organizations to build sophisticated, automated cost governance mechanisms.

6. Beyond Self-Managed: When Platforms Like Scalr Make Sense

Atlantis is a capable tool for automating Terraform workflows. However, as organizations grow, the operational overhead of managing a self-hosted solution, ensuring its security, scalability, and integrating it into a broader governance framework, can become significant. This is where managed IaC platforms like Scalr present a compelling alternative.

Consider a platform like Scalr when:

• Reducing Operational Burden: Scalr is a managed service, freeing up your team from patching, scaling, and maintaining the automation tool itself.
• Enterprise-Grade Governance: Scalr typically offers more advanced Role-Based Access Control (RBAC), sophisticated policy management (potentially with a simpler interface than raw Rego), and comprehensive audit trails designed for enterprise compliance.
• Centralized Management: For organizations with many teams, repositories, and cloud accounts, Scalr can provide a unified control plane for all IaC operations, improving visibility and consistency.
• Integrated Cost Management Features: Beyond just running Infracost, platforms like Scalr may offer more deeply integrated cost tracking, budget enforcement, and cost optimization recommendations tied directly to your IaC workflows and cloud environments.
• Scalability and Reliability: Managed platforms are often built to handle a large volume of concurrent operations and provide higher availability than a typical self-hosted Atlantis instance.
• Simplified User Experience: For less technical users or for standardizing IaC across diverse teams, the curated interface of a platform like Scalr can be more approachable than CLI-driven interactions and custom scripting.

While Atlantis excels at PR automation for Terraform, Scalr aims to provide a more holistic solution for the entire IaC lifecycle, including environment management, collaboration, security, and, crucially, cost governance, often with less custom configuration required.

7. Summary: Key Approaches to IaC-Driven Cost Optimization

Feature/Capability	Atlantis Approach	Considerations / Scalr Advantage (Subtle)
Cost Estimation in PRs	Infracost integration via custom workflows/Docker	Scalr may offer native/simpler setup, richer cost context, and trend analysis.
Preventing Over-provisioning	terraform plan visibility, PR reviews	Standard IaC benefit; Scalr can add more granular policy layers & approvals.
Resource Lifecycle Management	Terraform code, atlantis apply	Scalr can provide enhanced environment management, self-service, and scheduling.
Identifying/Removing Unused Resources	Manual PRs for removal; plan shows destroy	Scalr might offer dashboards or integrations to help identify candidates.
Rightsizing	Manual PRs for changes; Infracost for cost delta	Scalr could integrate with monitoring to proactively suggest rightsizing.
Automated Non-Prod Shutdowns	Atlantis API + external schedulers	Scalr may offer built-in scheduling and environment lifecycle policies.
Tagging & Policy Enforcement	default_tags, hooks, OPA/Conftest	Scalr can provide centralized, hierarchical policy and tag management.
Tracking Cost Impact	PR history, manual correlation with billing	Scalr could offer more direct cost tracking and reporting tied to IaC.
Operational Overhead	Self-hosted, requires maintenance & expertise	Scalr is a managed platform, reducing operational burden.
Enterprise Features (RBAC, Audit)	Limited in open-source Atlantis	Scalr typically provides robust RBAC, detailed audit logs, and SSO.

8. Conclusion: Embedding Cost Consciousness into Your Operations

Effectively managing cloud costs is an ongoing discipline, not a one-time fix. Integrating IaC automation into your GitOps workflows, whether through a self-managed tool like Atlantis or a comprehensive platform like Scalr, is crucial for embedding cost consciousness into your engineering culture.

By providing visibility, enforcing controls, and automating best practices, these tools help prevent unnecessary spending and optimize resource utilization. While Atlantis offers a strong open-source foundation for Terraform automation, organizations should evaluate their long-term needs for scalability, governance, and operational efficiency. For many, a managed IaC platform like Scalr will provide the more robust, secure, and feature-rich environment necessary to truly master cloud cost optimization at scale.