# Engines

## Understanding Engines in Workbench

An engine is an external service that executes WDL ( [Workflow Description Language](https://github.com/openwdl/wdl/blob/main/versions/1.0/SPEC.md) ) workflows in [Workbench](https://github.com/DNAstack/dnastack-product-docs/blob/main/docs/workbench/engines/broken-reference/README.md). These engines interpret your workflows, generate task definitions, and manage their execution in your chosen computing environment. You can [connect an engine](/products/workbench/engines/adding-and-updating-an-engine.md) running in your own environment to your Workbench account, which will then use that engine to submit and monitor workflow runs.

## How Engines Work

The engine is responsible for processing WDL, an open, community-driven workflow language stewarded by the [OpenWDL organization](https://openwdl.org). WDL is designed to be both easy to read and write, while scaling effectively from simple command-line tools to complex parallel workflows.

When you submit a workflow, your engine:

* Interprets the WDL script
* Generates individual task definitions
* Manages task dependencies and scheduling
* Dispatches tasks to execution services
* Handles resource allocation and management

Workflow engines that support WDL, such as Cromwell and miniWDL, provide these capabilities while managing the resources required for workflow execution.

## Supported Environments

You can run Workbench engines in various environments:

* [Amazon Web Services](/products/workbench/engines/adding-and-updating-an-engine/aws-healthomics.md)
* [Google Cloud Platform](/products/workbench/engines/adding-and-updating-an-engine/google-cloud-platform.md)
* [Microsoft Azure](/products/workbench/engines/adding-and-updating-an-engine/microsoft-azure.md)
* [On Premises](/products/workbench/engines/adding-and-updating-an-engine/on-premises.md)

## Viewing and Accessing Engines

Access your engines through either:

* The [Settings Page](https://workbench.omics.ai/settings) in the Workbench UI
* The [Command Line Interface](/products/command-line-interface/reference/workbench/engines-list.md) (CLI)

From the Settings page, use the search bar to find specific engines. Click any engine row to view detailed information about its state, configuration, and parameters.

## Default Engine Settings

The first engine you create in Workbench becomes your default engine. This default engine is pre-populated whenever you submit a workflow run, though you can change engines for specific runs. When submitting workflow runs from the CLI, the default engine is used if you omit the `--engine` flag.

To change your default engine:

1. Navigate to Settings
2. Hover over your chosen engine
3. Click the "Set as Default" star button

{% hint style="info" %}
You cannot delete the default engine. If you want to delete the default engine, you must first set another engine as the default.
{% endhint %}

## Actions

When viewing the engine list, hover over any row to access these actions:

#### **Edit Engine**

Clicking on the `Edit Engine` pencil icon button will allow you to update the engine configuration, engine name, and engine parameters

#### **Set as Default**

Clicking on the `Set as Default` star icon button will set the engine as the default engine in Workbench

#### **Copy Engine Id**

Clicking on the `Copy Engine Id` duplicate icon button will copy the engine ID to your clipboard. This is useful when you need to reference the engine ID in the CLI or API

#### **Delete Engine**

Clicking on the `Delete Engine` trashcan icon will remove the engine from Workbench.

{% hint style="danger" %}
This action is irreversible.
{% endhint %}

* You must set a new default before deleting a default engine
* Currently running workflows will be marked as failed but continue running
* The underlying infrastructure remains unaffected and must be deleted separately
* Previous runs remain visible but you cannot submit new runs or view logs

## Engine Status

Workbench continuously monitors connected engines to ensure availability. The system checks:

* **Connectivity** to API endpoints
* **Credential** authentication
* **Permission** verification
* **Storage** access
* **Log** streaming capability

Each engine runs only the checks relevant to its type and configuration. Failed checks put the engine in `ERROR` state until resolved, while passing checks keep it `ONLINE`. You can view engine status in the UI - a green dot indicates `ONLINE`, while a red dot shows `ERROR`. For troubleshooting help, consult your engine's configuration guide.


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