Description

Step Functions provide integration patterns to interact with services invoked. Waiting for a long-running process might lead users to build a polling workflows including control flows (e.g. Choice, Map, Wait) or calls made against other AWS services (e.g. LambdaInvoke). This would lead to the before architecture shown below where a Lambda function is invoked repeatedly after a specified wait period to continue with the workflow once the message was processed.

An example might look as follows:

Solution

Use Step Function's Callback Integration Pattern to call a service with a task token and have Step Functions wait until that token is returned with a payload.

See the CDK implementation of this pattern in Typescript on GitHub

Considerations

Advantages

• The Step function state machine workflow waits until the callback token is received. This abandons the need for a polling machanism and reduces the number of function integrations.

Applicability

• The Wait for a Callback with the Task Token Integration Pattern is available for supported services only.

Related Refactorings

• Extract Send Message