---
title: Run Queue
description: Learn how Terragrunt orchestrates multiple concurrent OpenTofu/Terraform runs.
slug: features/stacks/run-queue
sidebar:
  order: 5
---

import FileTree from '@components/vendored/starlight/FileTree.astro';
import { Aside, Tabs, TabItem } from '@astrojs/starlight/components';

Terragrunt's "Run Queue" is the mechanism it uses to manage the run order and concurrency when running OpenTofu/Terraform commands across multiple Terragrunt [units](/features/units). This is particularly relevant when using the [`run --all`](/reference/cli/commands/run#all) or [`run --graph`](/reference/cli/commands/run#graph) commands.

## How it Works: The Dependency Graph (DAG)

At its core, the Run Queue relies on a [Directed Acyclic Graph (DAG)](/getting-started/terminology#directed-acyclic-graph-dag) built from the dependencies defined between your Terragrunt units. These dependencies are typically established using [`dependency`](/reference/hcl/blocks#dependency) or [`dependencies`](/reference/hcl/blocks#dependencies) blocks in your `terragrunt.hcl` files.

Terragrunt analyzes these dependencies to determine the correct order of operations:

1.  **Discovery:** Terragrunt discovers configurations that might be relevant to a run based on the current working directory.
2.  **Constructing the Queue:** Based on the command being run, Terragrunt creates an ordered queue.
    *   For commands like `plan` or `apply`, dependencies are run *before* the units that depend on them.
    *   For commands like `destroy`, dependent units are run *before* their dependencies.
3.  **Runs:** Terragrunt dequeues the units in the queue and runs them, respecting the queue order. By default, it runs units concurrently up to a certain limit (controlled by the [`--parallelism`](/reference/cli/commands/run#parallelism) flag), but it will always wait for a unit's dependencies (or dependents for destroys) to complete successfully before running that unit.

### Example DAG

Consider a setup where:

- Unit "dependent" depends on unit "dependency".
- Unit "dependency" depends on unit "ancestor-dependency".
- Unit "independent" has no dependencies nor dependents.

<FileTree>

- root
  - subtree
    - dependent
      - terragrunt.hcl
    - dependency
      - terragrunt.hcl
  - ancestor-dependency
    - terragrunt.hcl
  - independent
    - terragrunt.hcl

</FileTree>


```d2
direction: right

# Define the nodes
dependent: dependent {
  shape: rectangle
}

dependency: dependency {
  shape: rectangle
}

ancestor-dependency: ancestor-dependency {
  shape: rectangle
}

independent: independent {
  shape: rectangle
}

# Define the connections
dependent -> dependency: depends on
dependency -> ancestor-dependency: depends on
```

Assuming a current working directory of the `root` directory, Terragrunt would run units in the following order:

-   **`run --all plan` Order:** Terragrunt would run `independent` and `ancestor-dependency` concurrently. Once `ancestor-dependency` finishes, `dependency` would run. Once `dependency` finishes, `dependent` would run.
-   **`run --all destroy` Order:** Terragrunt would run `dependent` and `independent` concurrently. Once `dependent` finishes, `dependency` would run. Once `dependency` finishes, `ancestor-dependency` would run.

## Controlling the Queue

Several flags allow you to customize how Terragrunt builds and executes the run queue. By default, Terragrunt will include all units that are in the current working directory.

### Include by default

By default, when using the `--all` flag, Terragrunt will include all units that are in the current working directory.

Using any positive filter triggers "Exclude by default" behavior, meaning that Terragrunt will no longer automatically include all units in the current working directory, and will instead selectively include units only if they match a positive filter (and don't match any negative filters).

More on this in the [Filtering Units](#filtering-units) section.

### Filtering Units

You can control which units are included or excluded from the queue using the [`--filter` flag](/features/filter).

#### Positive Filters

Any filter that doesn't start with a `!` prefix is considered a positive filter. When Terragrunt sees that any positive filter is present, it will evaluate every path it encounters while walking the directory tree, and only include units that match a positive filter.

```bash
terragrunt run --all --filter './subtree/**' -- plan
```

This will tell Terragrunt only to run the units that match the glob pattern `./subtree/**` (any directory found in the current working directory starting with `subtree`).

There are many more types of filters you can use, and those details are covered in the [Filter feature documentation](/features/filter).

#### Negative Filters

Any filter that starts with a `!` prefix is considered a negative filter. Negative filters are always evaluated after positive filters (if present).

```bash
terragrunt run --all --filter '!./subtree/**' -- plan
```

This will tell Terragrunt to run all units in the current working directory except those that match the glob pattern `./subtree/**` (any directory found in the current working directory starting with `subtree`).

#### Combining Positive and Negative Filters

You can combine positive and negative filters to ensure that only the units you want are run.

```bash
terragrunt run --all --filter './subtree/**' --filter '!./subtree/dependency/**' -- plan
```

This will tell Terragrunt to run all units in the directory `subtree` except those that match the glob pattern `./subtree/dependency/**` (any directory found in the current working directory starting with `subtree/dependency`).

### Modifying Order and Error Handling

- [`--queue-construct-as`](/reference/cli/commands/list#queue-construct-as) (`--as`): Build the run queue *as if* a particular command was run. Useful for performing dry-runs of [`run`](/reference/cli/commands/run) using discovery commands, like [`find`](/reference/cli/commands/find) and [`list`](/reference/cli/commands/list).

  e.g. `terragrunt list --queue-construct-as destroy`

  This lists the units in the order they'd be processed for `run --all destroy`:

  ```bash
  $ terragrunt list --as destroy -l
  Type  Path
  unit  independent
  unit  subtree/dependent
  unit  subtree/dependency
  unit  ancestor-dependency
  ```

  ```bash
  $ terragrunt list --as plan -l
  Type  Path
  unit  ancestor-dependency
  unit  independent
  unit  subtree/dependency
  unit  subtree/dependent
  ```

- [`--queue-ignore-dag-order`](/reference/cli/commands/run#queue-ignore-dag-order): Run units in the queue concurrently without respecting the dependency order.

  e.g. `terragrunt run --all plan --queue-ignore-dag-order`

  Run `plan` on `ancestor-dependency`, `subtree/dependency`, `subtree/dependent`, and `independent` all concurrently, without waiting for their defined dependencies. For instance, `subtree/dependent`'s plan would not wait for `subtree/dependency`'s plan to complete.

  <Aside type="caution">
  This flag is useful for faster runs in stateless commands like `validate` or `plan`, but is **dangerous** for commands that modify state like `apply` or `destroy`.

  You might encounter failed applies if unit dependencies are not applied before dependents, and conversely, failed destroys if unit dependents are not destroyed before dependencies.
  </Aside>

- [`--queue-ignore-errors`](/reference/cli/commands/run#queue-ignore-errors): Continue processing the queue even if some units fail.

  e.g. `terragrunt run --all plan --queue-ignore-errors`

  If `ancestor-dependency`'s plan fails, Terragrunt will still attempt to run `plan` for `subtree/dependency`, then `subtree/dependent`, and also for `independent`.

  <Aside type="caution">
  This flag is useful for identifying all errors at once, but can lead to inconsistent state if used with `apply` or `destroy`.

  You might encounter failed applies if unit dependencies are not applied successfully before dependents, and conversely, failed destroys if unit dependents are not destroyed successfully before dependencies.
  </Aside>

- [`--fail-fast`](/reference/cli/commands/run#fail-fast): Fail the run if any unit fails, stopping all remaining units immediately.

  e.g. `terragrunt run --all plan --fail-fast`

  If `independent`'s plan fails, Terragrunt will stop running any more units and fail the run, even if `ancestor-dependency`'s plan succeeds.

  <Aside type="tip">
  This flag is useful when you want to fail the run as soon as any unit fails, and stop running any more units.
  </Aside>

## Important Considerations

<Aside type="caution">
When using `run --all plan` with units that have dependencies (e.g. via `dependency` or `dependencies` blocks), the command will fail if those dependencies have never been deployed. This is because Terragrunt cannot resolve dependency outputs without existing state.

To work around this issue, use [mock outputs in dependency blocks](/reference/hcl/blocks/#dependency).
</Aside>

<Aside type="caution">
Do not set `TF_PLUGIN_CACHE_DIR` when using `run --all` (unless using OpenTofu >= 1.10).

This can cause concurrent access issues with the provider cache. Instead, use Terragrunt's built-in [Provider Cache Server](/features/caching/provider-cache-server/).
</Aside>

<Aside type="caution">
When using `run --all` with `apply` or `destroy`, Terragrunt automatically adds the `-auto-approve` flag due to limitations with shared stdin making individual approvals impossible. Use [`--no-auto-approve`](/reference/cli/commands/run#no-auto-approve) to override this, but be aware you might need alternative approval workflows.
</Aside>
