Wait using callbacks

Callbacks allow workflow executions to wait for another service to make a request to the callback endpoint; that request resumes the execution of the workflow.

With callbacks, you can signal to your workflow that a specified event has occurred, and wait on that event without polling. For example, you can create a workflow that notifies you when a product is back in stock or when an item has shipped; or that waits to allow human interaction such as reviewing an order or validating a translation.

This page shows you how to create a workflow that supports a callback endpoint, and that waits for HTTP requests from external processes to arrive at that endpoint. You can also wait for events using callbacks and Eventarc triggers.

Callbacks require the use of two standard library built-in functions:

• events.create_callback_endpoint—Creates a callback endpoint expecting the specified HTTP method
• events.await_callback—Waits for a callback to be received at the given endpoint

Create an endpoint that receives a callback request

Create a callback endpoint that can receive HTTP requests to arrive at that endpoint.

1. Follow the steps to create a new workflow, or choose an existing workflow to update but don't deploy it yet.
2. In the workflow's definition, add a step to create a callback endpoint:

   YAML

       - create_callback:
           call