terragrunt.stack.hcl

import Since from '@components/Since.astro'; import Before from '@components/Before.astro'; import { Aside } from '@astrojs/starlight/components';

Support for the autoinclude block in terragrunt.stack.hcl files, enabling dependency relationships and configuration overrides during stack generation.

stack-dependencies - What it does

When enabled, this experiment adds support for the autoinclude block nested inside unit and stack blocks in terragrunt.stack.hcl files. The autoinclude block allows users to define dependency blocks and arbitrary configuration that gets generated into a terragrunt.autoinclude.hcl file during stack generation. This file is automatically merged into the unit/stack configuration when parsed.

This experiment enables:

• unit.<name>.path and stack.<name>.path variables in terragrunt.stack.hcl for referencing sibling component paths
• stack.<name>.<unit_name>.path for referencing individual units within a nested stack (fine-grained dependency)
• dependency blocks targeting stack directories — aggregated outputs from all units in the stack (dependency.stack_name.outputs.unit_name.output_key)
• Automatic deep merge of terragrunt.autoinclude.hcl into unit configurations (autoinclude wins)
• Stack dependency expansion in the run queue — depending on a stack blocks until all its units complete

Unit-to-unit dependencies within a stack

# terragrunt.stack.hcl
unit "vpc" {
  source = "../catalog/units/vpc"
  path   = "vpc"
}

unit "app" {
  source = "../catalog/units/app"
  path   = "app"

  autoinclude {
    dependency "vpc" {
      config_path = unit.vpc.path
    }

    inputs = {
      vpc_id = dependency.vpc.outputs.vpc_id
    }
  }
}

Dependencies on units within a nested stack

# terragrunt.stack.hcl
stack "stack_w_outputs" {
  source = "../catalog/stacks/stack-w-outputs"
  path   = "stack-w-outputs"
}

unit "unit_w_inputs" {
  source = "../catalog/units/unit-w-inputs"
  path   = "unit-w-inputs"

  autoinclude {
    dependency "unit_w_outputs" {
      config_path = stack.stack_w_outputs.unit_w_outputs.path

      mock_outputs_allowed_terraform_commands = ["plan"]
      mock_outputs = {
        val = "fake-val"
      }
    }

    inputs = {
      val = dependency.unit_w_outputs.outputs.val
    }
  }
}

Dependencies on entire stacks

# terragrunt.stack.hcl
stack "infra" {
  source = "../catalog/stacks/infra"
  path   = "infra"
}

unit "app" {
  source = "../catalog/units/app"
  path   = "app"

  autoinclude {
    dependency "infra" {
      config_path = stack.infra.path
    }

    inputs = {
      vpc_id = dependency.infra.outputs.vpc.vpc_id
    }
  }
}

terragrunt run --all --experiment stack-dependencies -- plan

stack-dependencies - How to provide feedback

Provide your feedback on the Stack Dependencies RFC GitHub Issue.

stack-dependencies - Implementation roadmap

• Create internal/hclparse package with two-phase stack file parser and autoinclude data structures
• Implement terragrunt.autoinclude.hcl file generator with relative path resolution
• Implement AST-walking partial evaluator for mixed local.* + dependency.* expressions
• Integrate autoinclude parsing and generation into pkg/config/stack.go stack generation pipeline
• Auto-merge terragrunt.autoinclude.hcl into unit config during ParseConfig() with deep merge
• Add tryGetStackOutput() for dependency blocks targeting stack directories
• Add ExtractAutoIncludeDependencyPaths() so DAG sees dependencies from autoinclude files
• Add integration tests and test fixtures for end-to-end validation
• E2E validation with stack run apply and stack run destroy
• Community feedback on autoinclude syntax and merge behavior
• Integration with CAS for generated files
• Performance validation at scale

• Create internal/hclparse package with two-phase stack file parser and autoinclude data structures
• Implement terragrunt.autoinclude.hcl file generator with relative path resolution
• Implement AST-walking partial evaluator for mixed local.* + dependency.* expressions
• Integrate autoinclude parsing and generation into pkg/config/stack.go stack generation pipeline
• Auto-merge terragrunt.autoinclude.hcl into unit config during ParseConfig() with deep merge
• Add tryGetStackOutput() for dependency blocks targeting stack directories
• Add ExtractAutoIncludeDependencyPaths() so DAG sees dependencies from autoinclude files
• Add integration tests and test fixtures for end-to-end validation
• E2E validation with stack run apply and stack run destroy
• Community feedback on autoinclude syntax and merge behavior
• Integration with CAS for generated files
• Performance validation at scale