Build a custom workflow in System Image Utility on Mac
Use image workflows to create macOS NetBoot, NetInstall, and NetRestore images. Workflows let you manually define the contents of your image in System Image Utility.
You must be logged in as an administrator user to build a custom workflow. Actions in a workflow must be connected; if they aren’t, the workflow is invalid and the actions are not processed.
To build a workflow from a set of actions, drag and drop the actions from the Automator Library in the sequence in which you want them to run. Each action in the workflow corresponds to a step you would usually have to perform manually.
Each action has options and settings you can configure. System Image Utility connects these action components with the types of data that are flowing from one action to another.
Custom workflows must begin with a Define Image Source action and end with a Create Image action.
Open System Image Utility for me
In the System Image Utility app
on your Mac, click the Source pop-up menu, choose your configured Mac volume, mounted disk image (which also appears as a configured Mac volume), or macOS install app, then click Next.In the Network Disk Image pane, choose the type of image you want to create.
Click the Customize button to open the Automator app.
An untitled workflow opens, with a Define Image Source action included as the first step in the workflow.
In the Automator app
, choose View > Arrange Actions by > Application, then click System Image Utility in the Automator Library.In the Define Image Source action, click the Source pop-up menu, then choose the image source.
From the Automator Library, choose additional actions you need, then drag them into the Workflow area below the Define Image Source action.
Arrange the actions in the order you like, configuring each action as you go.
Select the Create Image action in the Automator Library, drag it to the end of your workflow, then read the Software License Agreement. If you agree, click Agree to continue.
Configure the Create Image action:
Select the type of image you want to create.
If you’re creating a NetBoot or NetRestore image, enter a name in the Installed Volume field. This becomes the name of the volume on which your image is installed.
(Optional) If you’re creating a NetRestore image, select “Include macOS Recovery partition.”
Click the Save To pop-up menu, then choose where to save the image.
In the Image Name field, enter the name of the image file. This name identifies the image file stored on the computer.
In the Network Disk field, enter a name for your image. This name identifies the image in the Startup Disk preferences pane on client computers.
(Optional) In the Description field, enter notes or other information to help you characterize the image. The description information doesn’t appear on the client Mac.
In the Image Index field, enter an Image ID:
To create an image that is unique to this server, enter an ID in the range 1–4095.
To create one of several identical images to be stored on different servers, enter an ID in the range 4096–65535.
Note: Multiple network images of the same type with the same ID in the 4096–65535 range are displayed as a single startup image in a client’s Startup Disk preferences pane.
If you want to save the workflow to reuse later, click Untitled.workflow in the title bar, then enter a name and location for the workflow.
To start the workflow, click Run, then authenticate if necessary.
Important: Do not attempt to edit content in the image destination folder while the image is being created.
You can also use the automator command in the Terminal app 
to run a workflow. Enter the following command to run a workflow with somevariable set to somevalue in the myworkflow.workflow file:
$ automator -D somevariable=somevalue myworkflow.workflow