Subflows and Actions in Flow Designer

Subflows and Actions in Flow Designer – A Complete Guide for ServiceNow CAD Exam

Introduction

Flow Designer is a powerful automation engine in ServiceNow that allows developers and administrators to build complex workflows without extensive scripting. Two of the most critical building blocks in Flow Designer are Subflows and Actions. Understanding these components is essential for anyone preparing for the ServiceNow Certified Application Developer (CAD) exam, as they form the backbone of application automation on the platform.

Why Are Subflows and Actions Important?

Subflows and Actions are important for several reasons:

1. Reusability: Both subflows and actions promote the DRY (Don't Repeat Yourself) principle. Once created, they can be reused across multiple flows, reducing duplication and maintenance overhead.

2. Modularity: They allow developers to break down complex automation logic into smaller, manageable, and testable units.

3. Standardization: Organizations can create standardized actions and subflows that enforce best practices and consistent behavior across applications.

4. Low-Code Development: Actions and subflows empower citizen developers and administrators to build automations using a visual interface rather than writing complex scripts.

5. Maintainability: When a change is needed, updating a single action or subflow propagates the change to every flow that references it.

What Are Actions in Flow Designer?

An Action is the most granular reusable component in Flow Designer. It represents a single operation or task that can be performed as part of a flow or subflow. Think of actions as the individual steps or building blocks that perform specific work.

Key Characteristics of Actions:

- Actions are designed to perform a single, specific operation (e.g., create a record, send an email, make a REST call, look up a record, update a record).
- Actions have Inputs (data they receive), processing steps (the logic they execute), and Outputs (data they return to the calling flow or subflow).
- Actions can contain script steps, allowing developers to include custom JavaScript when the built-in no-code steps are insufficient.
- ServiceNow provides many out-of-the-box (OOTB) actions such as Create Record, Update Record, Look Up Records, Send Email, Ask for Approval, and many more.
- Developers can create custom actions to encapsulate unique business logic.
- Actions are categorized and can be published to make them available across the platform.
- Actions support Action Designer, a dedicated interface for building and testing actions.

Structure of an Action:

- Inputs: Define what data the action needs to function. Inputs can be mandatory or optional and have defined data types.
- Steps: The logic within the action. Steps can include script steps, flow logic steps, or calls to other actions.
- Outputs: The data the action returns after execution. Outputs are available to subsequent steps in the parent flow or subflow as data pills.

What Are Subflows in Flow Designer?

A Subflow is a reusable sequence of actions, flow logic, and other subflows that can be called from a parent flow or another subflow. Subflows are essentially mini-flows that encapsulate a series of steps into a single callable unit.

Key Characteristics of Subflows:

- Subflows contain multiple steps, including actions, flow logic (if/else, for each loops, etc.), and even other subflows.
- Like actions, subflows have Inputs and Outputs.
- Subflows do NOT have triggers. They are always invoked by a parent flow or another subflow. This is a critical distinction from flows, which are initiated by triggers.
- Subflows promote reusability at a higher level than actions. While actions perform single tasks, subflows orchestrate multiple tasks together.
- Subflows can be published and made available to other developers and across multiple applications.
- They support error handling within their step sequences.

Key Differences Between Subflows and Actions

Understanding the differences is crucial for the CAD exam:

1. Scope of Work: An action performs a single, specific task. A subflow orchestrates multiple actions and logic into a reusable process.

2. Triggers: Neither actions nor subflows have triggers. Only Flows have triggers. Subflows and actions are invoked from within flows or other subflows.

3. Complexity: Actions are simpler and more atomic. Subflows are more complex and represent a sequence of operations.

4. Flow Logic: Subflows can contain flow logic elements such as If/Else conditions, For Each loops, and Do the following in parallel. Actions contain action steps (script steps, etc.) but not flow-level logic in the same way.

5. Use Case: Use an action when you need to perform a discrete operation. Use a subflow when you need to group a series of actions and logic together for reuse.

6. Nesting: A subflow can call other subflows and actions. An action typically does not call subflows (though it can call other actions internally via script).

How Subflows and Actions Work Together

In practice, the architecture follows a hierarchy:

Flow (with Trigger) → calls → Subflows → calls → Actions

A Flow is the top-level automation. It starts with a trigger (e.g., when a record is created, on a schedule, or when triggered by a REST API). Inside the flow, you add steps which can be:

- Individual Actions (e.g., Look Up Record, Create Record)
- Subflows (e.g., an Approval Process subflow that contains multiple actions and logic)
- Flow Logic (If/Else, For Each, Do the Following in Parallel)

The subflows in turn call actions and can contain their own flow logic. This hierarchical structure allows for clean, modular, and maintainable automation design.

How to Create a Custom Action

1. Navigate to Flow Designer and click New → Action.
2. Provide a name and description for the action.
3. Select the application scope.
4. Define Inputs — specify the data the action will receive (name, type, mandatory/optional).
5. Add Steps — these can be script steps, record operations, or other predefined steps.
6. Define Outputs — specify what data the action returns.
7. Test the action using the built-in testing capability.
8. Publish the action to make it available for use in flows and subflows.

How to Create a Subflow

1. Navigate to Flow Designer and click New → Subflow.
2. Provide a name and description.
3. Select the application scope.
4. Define Inputs — the data the subflow needs from its caller.
5. Add Actions, other Subflows, and Flow Logic as steps.
6. Define Outputs — the data to return to the calling flow.
7. Test the subflow.
8. Publish the subflow.

Data Pills in Flow Designer

A key concept to understand is data pills. When an action or subflow produces outputs, those outputs become available as data pills that can be dragged into input fields of subsequent steps. This is how data flows between steps in Flow Designer. The outputs of one action become the inputs of the next, creating a data pipeline throughout the flow.

Error Handling

Both actions and subflows support error handling:

- Try/Catch blocks can be used in flow logic to handle errors gracefully.
- Actions with script steps can include error handling within the script.
- If an action or subflow fails, the error can be caught and alternative logic can be executed.

Publishing and Versioning

- Actions and subflows must be published before they can be used in other flows and subflows.
- Once published, changes require creating a new version (or editing and republishing).
- This versioning approach ensures that existing flows are not broken by changes to shared components.

Spokes

Related actions and subflows are grouped into Spokes. A spoke is essentially an application or integration package that contains a collection of related Flow Designer actions and subflows. For example, the ITSM spoke contains actions related to IT Service Management processes. Understanding spokes helps contextualize where actions and subflows are organized.

Common Out-of-the-Box Actions

- Create Record: Creates a new record in a specified table.
- Update Record: Updates fields on an existing record.
- Look Up Record: Retrieves a single record based on conditions.
- Look Up Records: Retrieves multiple records based on conditions.
- Delete Record: Deletes a specified record.
- Send Email: Sends an email notification.
- Ask for Approval: Initiates an approval request.
- Create Task: Creates a task record.
- Log: Logs a message for debugging purposes.
- Wait for Condition: Pauses the flow until a specified condition is met.

Common Out-of-the-Box Subflows

ServiceNow provides several OOTB subflows, often related to approval processes, notifications, and ITSM workflows. These can be used directly or serve as templates for custom subflows.

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Exam Tips: Answering Questions on Subflows and Actions in Flow Designer

Here are targeted tips to help you succeed on the ServiceNow CAD exam when questions involve subflows and actions:

1. Know the Key Distinction: Flows vs. Subflows vs. Actions
- Flows have triggers and are the top-level automation.
- Subflows do NOT have triggers; they are called from flows or other subflows.
- Actions are the smallest reusable units that perform a single operation.
- If a question asks what component has a trigger, the answer is always Flow, never subflow or action.

2. Remember: Subflows Are for Reusable Multi-Step Logic
- If a question describes a scenario where multiple steps need to be reused across different flows, the answer is likely Subflow.
- If the scenario describes a single reusable operation, the answer is likely Action.

3. Understand Inputs and Outputs
- Both actions and subflows accept inputs and produce outputs.
- Outputs become data pills available to downstream steps.
- Exam questions may test whether you understand how data is passed between components.

4. Publishing Is Required
- Remember that actions and subflows must be published before they are available for use.
- If a question asks why an action or subflow is not appearing as an option, the likely answer is that it has not been published.

5. Actions Can Contain Script Steps
- Custom actions can include script steps for advanced logic.
- This is a key advantage when OOTB capabilities are not sufficient.
- Exam questions may ask about when to use a script step inside an action.

6. Understand Spokes
- Know that spokes are collections of related actions and subflows.
- IntegrationHub spokes extend Flow Designer with third-party integrations.
- If a question mentions integrating with an external system using Flow Designer, think about spokes and IntegrationHub.

7. Error Handling
- Know that Flow Designer supports Try/Catch error handling.
- Questions may present scenarios where a flow needs to handle failures gracefully.

8. Look for Keywords in Questions
- "Reusable sequence of steps" → Subflow
- "Single reusable operation" → Action
- "Triggered by a record change" → Flow (with a trigger)
- "Called from within a flow" → Could be either Subflow or Action, but context will clarify.
- "No trigger" → Subflow or Action

9. Understand When to Use Flow Designer vs. Workflow
- ServiceNow is moving toward Flow Designer as the preferred automation tool over legacy Workflow.
- Flow Designer offers a more modern, no-code/low-code interface.
- Exam questions may compare the two; know that Flow Designer is the recommended approach for new development.

10. Practice in a PDI (Personal Developer Instance)
- The best way to prepare is hands-on practice. Create custom actions, build subflows, and wire them into flows in your PDI.
- Test the publishing process, experiment with data pills, and try error handling.

11. Scope Matters
- Actions and subflows are created within a specific application scope.
- They are accessible based on scope settings (whether they are accessible from other scopes).
- Exam questions may touch on scope-related visibility of actions and subflows.

12. Process of Elimination
- On multiple-choice questions, eliminate answers that confuse flows with subflows (e.g., an answer that says subflows have triggers).
- Eliminate answers that suggest actions contain flow logic like If/Else branching at the flow level.

Summary

Subflows and Actions are foundational concepts in Flow Designer that every ServiceNow developer must master. Actions are atomic, single-purpose operations, while subflows orchestrate multiple actions and logic into reusable processes. Together, they enable modular, maintainable, and scalable automation. For the CAD exam, focus on understanding their differences, when to use each, how data flows between them via data pills, and the requirement to publish them before use. Hands-on practice in a PDI will solidify your understanding and give you the confidence to answer exam questions accurately.