What Sets Them Apart
Terragrunt and Atlantis solve adjacent but distinct problems in Terraform-based infrastructure management. Terragrunt wraps the Terraform CLI to eliminate code duplication across environments and modules through a hierarchical HCL configuration system. Atlantis operates as a webhook-driven server that watches pull requests and automatically runs terraform plan when infrastructure code changes, posting the output directly in the PR for team review before anyone types terraform apply.
Terragrunt and Atlantis at a Glance
The configuration management approach differs fundamentally. Terragrunt uses terragrunt.hcl files that inherit settings from parent directories, allowing teams to define common backend configurations, provider settings, and variable values once and override them per environment. Without Terragrunt, teams typically duplicate backend blocks and variable definitions across every module directory. Atlantis does not address configuration duplication at all; it assumes Terraform modules are already organized and focuses on automating when and how those modules execute.
The collaboration model reveals the clearest distinction. Atlantis turns infrastructure changes into a code review workflow where terraform plan runs automatically on every PR, team members review the planned changes alongside the code diff, and terraform apply executes only after approval. This prevents direct apply from developer workstations and creates an audit trail in version control. Terragrunt can be used in this same PR workflow when combined with CI/CD tools, but does not provide the PR automation natively.
Dependency management is a core Terragrunt capability that has no equivalent in Atlantis. Terragrunt resolves cross-module dependencies through dependency blocks and the terragrunt_output function, ensuring modules execute in the correct order and can reference outputs from other modules. Atlantis processes each module independently based on which files changed in the PR, without awareness of inter-module relationships unless explicitly configured through server-side project definitions.
Stack Orchestration, PR Workflow, and DRY Patterns
The 1.0 release of Terragrunt introduced stacks for grouping related infrastructure components into deployable units, filters for selective execution across monorepos, and run reports for tracking changes across multi-module operations. These features address the orchestration complexity that grows as infrastructure codebases scale beyond a handful of modules. Atlantis has remained focused on its core PR automation workflow, with customization through server-side configuration and custom workflow definitions.
Locking and concurrency control take different approaches. Atlantis provides built-in workspace locking that prevents concurrent applies to the same infrastructure, avoiding state conflicts when multiple team members work on overlapping resources. Terragrunt relies on the backend state locking provided by Terraform itself through DynamoDB or similar mechanisms, without adding an additional coordination layer for human workflow management.
Self-hosting requirements differ substantially. Atlantis requires running a persistent server that receives webhooks from GitHub, GitLab, or Bitbucket, with network access to the Terraform state backend and cloud provider APIs. Terragrunt is a pure CLI tool that runs wherever Terraform runs, including developer laptops, CI runners, and ephemeral build environments with no persistent infrastructure requirements. The operational overhead of Atlantis is higher but provides proportionally more workflow automation.
Ecosystem Integration and Team Workflow
The ecosystem integration patterns complement rather than compete. Many teams run Terragrunt inside Atlantis, using Terragrunt for configuration management and dependency resolution while Atlantis handles the PR automation and team collaboration workflow. This combination gives teams DRY configurations from Terragrunt plus automated plan and apply from Atlantis, addressing both code organization and workflow automation in a single stack.
Cost management integration exists in Terragrunt through Terragrunt Scale, which adds a free CI/CD tier with run reports and execution visibility. Atlantis does not include native cost estimation but integrates with tools like Infracost through custom workflow steps that can add cost impact information to PR comments alongside the terraform plan output. Both approaches enable cost-aware infrastructure changes, but through different integration mechanisms.
