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Dependency-Ordered Execution for Terraform --all Flag

· 3 min read
Erik Osterman
Erik Osterman
Founder @ Cloud Posse

The --all flag now executes Terraform components in dependency order. Run atmos terraform apply --all -s ue2-dev and components are automatically processed based on their depends_on relationships.

What Changed​

The --all flag for terraform commands now respects component dependencies defined in your stack configurations. Components are executed in topological order, ensuring dependencies are processed before dependents.

# Components execute in dependency order
$ atmos terraform apply --all -s ue2-dev

Executing: atmos terraform apply vpc -s ue2-dev
Executing: atmos terraform apply rds -s ue2-dev      # depends on vpc
Executing: atmos terraform apply eks -s ue2-dev      # depends on vpc
Executing: atmos terraform apply app -s ue2-dev      # depends on rds, eks

Previously, --all processed components in an arbitrary order, which could cause failures when a component was applied before its dependencies.

Why This Matters​

Reliable Infrastructure Deployments​

When deploying a complete environment, component order matters. A database component that references a VPC's subnet IDs will fail if the VPC hasn't been created yet. Dependency ordering eliminates these race conditions.

# stacks/ue2-dev.yaml
components:
  terraform:
    rds:
      settings:
        depends_on:
          - component: vpc
    eks:
      settings:
        depends_on:
          - component: vpc
    app:
      settings:
        depends_on:
          - component: rds
          - component: eks

Destroy in Reverse Order​

The destroy command automatically reverses the dependency order, ensuring dependents are destroyed before their dependencies:

$ atmos terraform destroy --all -s ue2-dev

Executing: atmos terraform destroy app -s ue2-dev    # destroyed first
Executing: atmos terraform destroy eks -s ue2-dev
Executing: atmos terraform destroy rds -s ue2-dev
Executing: atmos terraform destroy vpc -s ue2-dev    # destroyed last

Circular Dependency Detection​

The system detects circular dependencies and fails fast with a clear error message:

$ atmos terraform apply --all -s ue2-dev

Error: circular dependency detected: vpc -> rds -> app -> vpc

How It Works​

Dependency Graph Construction​

When you run a command with --all, Atmos:

  1. Discovers components - Finds all Terraform components in the specified stack
  2. Builds dependency graph - Parses depends_on settings to create a directed acyclic graph (DAG)
  3. Topological sort - Orders components so dependencies come before dependents
  4. Executes in order - Runs the terraform command for each component sequentially

Cross-Stack Dependencies​

Dependencies can reference components in other stacks:

components:
  terraform:
    app:
      settings:
        depends_on:
          - component: vpc
            stack: ue2-network  # Different stack

Dry Run Support​

Preview execution order without making changes:

$ atmos terraform apply --all -s ue2-dev --dry-run

Would execute: atmos terraform apply vpc -s ue2-dev
Would execute: atmos terraform apply rds -s ue2-dev
Would execute: atmos terraform apply eks -s ue2-dev
Would execute: atmos terraform apply app -s ue2-dev

Usage​

The --all flag requires a stack to be specified:

# Apply all components in a stack
atmos terraform apply --all -s ue2-dev

# Plan all components
atmos terraform plan --all -s ue2-prod

# Destroy all components (reverse order)
atmos terraform destroy --all -s ue2-staging

Combining with Queries​

Filter which components to include using the --query flag:

# Apply only components matching a query
atmos terraform apply --all -s ue2-dev --query '.settings.team == "platform"'

Get Involved​