---
title: Overview
---

Workflows, as part of the Application, can glue together additional delivery processes and specify arbitrary delivery environments. In short, `Workflow` provides customized control flow and flexibility based on the original delivery model of Kubernetes(Apply). For example, `Workflow` can be used to implement complex operations such as pause, manual approval, if conditions, waiting status, data flow, multi-environment gray release, A/B testing, etc.

A workflow consists of multiple steps, and typical workflow steps include step groups (containing a series of sub-steps), human review, multi-cluster publishing, notifications, etc. You can view all built-in workflow steps provided by default in KubeVela in [built-in workflow steps](./built-in-workflow-defs.md). If the built-in workflow steps don't meet your needs, you can also [custom workflow steps](../../platform-engineers/workflow/workflow.md).

`Workflow` consists of steps, you can either use KubeVela's [built-in workflow steps](./built-in-workflow-defs.md) like `suspend`, `notification`, `deploy`, `step-group` etc, or [customize your own `WorkflowStepDefinition`](../../platform-engineers/workflow/workflow.md).

In fact, if you only use components in the Application and do not declare a workflow, KubeVela will automatically create a default workflow for deploying the components when running the Application.

In VelaUX, you can feel the workflow more intuitively. As shown in the figure: The following is a workflow where the first step succeeds and the second fails:

![velaux-workflow](../../resources/velaux-workflow.png)

## Execution order

In the workflow, all the steps will be executed sequentially and the next step will be executed after the previous one succeeded. If a step is of type `step-group`, it can contain a series of sub-steps, all of which are executed together when the step group is executed.

In KubeVela 1.5.0+, you can explicitly specify the execution mode of steps, such as:

```yaml
workflow:
  mode:
    steps: StepByStep
    subSteps: DAG
```

There're two modes of execution: StepByStep and DAG.
 
If you do not explicitly declare the execution mode, by default steps are executed sequentially in StepByStep and subSteps are executed in parallel in DAG.

## State of Application and Workflow

|    Application     |  Workflow  |                                                   Description                                                    |
| :----------------: | :--------: | :--------------------------------------------------------------------------------------------------------------: |
|  runningWorkflow   | executing  |                 When the workflow is executing, the status of the application is runningWorkflow                 |
| workflowSuspending | suspending |               When the workflow is suspended, the status of the application is workflowSuspending                |
| workflowTerminated | terminated |               When the workflow is terminated, the status of the application is workflowTerminated               |
|   workflowFailed   |   failed   | When a step in the workflow fails and the workflow is completed, the status of the application is workflowFailed |
|      running       | succeeded  |        When all steps in the workflow are executed successfully, the status of the application is running        |

## Core features

Workflow has powerful process control capabilities, including:

- View [Workflow Operations](./operations.md) to learn how to operate the workflow.
- View [Suspend and Resume Workflow](./suspend.md) to learn how to suspend and resume a workflow.
- View [Sub Steps](./step-group.md) to learn how to use sub-steps in the workflow.
- View [Dependency](./dependency.md) to learn how to specify dependencies for workflow steps.
- View [Pass data between steps](./inputs-outputs.md) to learn how to use `inputs`, `outputs` to pass data between steps.
- View [If Conditions](./if-condition.md) to learn how to use `if` to determine whether the step should be executed.
- View [Timeout Steps](./timeout.md) to learn how to set `timeout` for steps.
- View [Debug Workflow](../../platform-engineers/debug/debug.md) to learn how to debug workflow in the real environment.