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Suspend and Resume

Flows can be suspended until resumed or cancelled event(s) are received. This feature is most useful to implement approval steps but can be used for other purposes as well.

Add Approval Script

Adding approval step

You can think of a scenario where only specific people can resume or cancel a Flow. To achieve this they would need to receive a personalized URL via some external communication channel (like e-mail, SMS or chat message).

Important thing to remember is that the number of required approvals can be customized. This allows some flexibility for cases where you either require approvals from all authorized people or only from one.

Required approvals

Example with Gmail

Add Gmail Resource

Lets start with adding a Gmail Resource. On the Resources page, click "Add a resource/API", select the gmail OAuth API and click "Sign in with Google".


As Google is an OAuth provider, you will be redirected to select your Google account. To make the Approval Script work, you need to sign in and allow Windmill to send e-mails on your behalf.

Connect the Gmail API

Save the Gmail Resource

Reusing Script from Windmill Hub

Let's create a Flow as described in the getting started section. Our first step will be an Approval Script from Windmill Hub, so click the + sign in the left pane and select "Approval (Script)".

Add Approval step

Once the step is added, you'll be presented with some pre-made Scripts from the Hub. Select the one named "Suspend/resume a flow by sending approval URL via email (gmail)".

Reuse Gmail script from Hub

Make sure to fill required fields: for gmail_auth, select your newly added Gmail resource and define email addresses in the approver_emails input.

Enter Script arguments

Run the Flow

For the sake of this example let's add a "dummy" Script as a second step in our Flow.

Dummy script

The Flow is now ready for testing, let's click "Test flow" in the top-right corner.

Running the Flow

You can notice that after the first step, the Flow is suspended and is waiting for approval. An e-mail should have been sent to the email addresses you specified. It contains a link to a webpage that looks like the following:

Waiting for approval

Let's approve and resume the Flow and see that it has successfully ran the second step as well.

Finished flow