Step Functions is often used to poll long-running processes, e.g. when starting a new data migration task with Amazon Database Migration. There's usually a Wait -> Poll -> Choice loop that runs until the task is complete (or failed), like the one below. Polling is inefficient and can add unnecessary cost as standard workflows are charged based on the number of state transitions. There is an event-driven alternative to this approach. Here's the high level approach: To start the data migration,...

Lambda Durable Functions comes with a handy testing SDK. It makes it easy to test durable executions both locally as well as remotely in the cloud. I find the local test runner particular useful for dealing with wait states because I can simply configure the runner to skip time! However, this does not work for callback operations such as waitForCallback. Unfortunately, the official docs didn't include any examples on how to handle this. So here's my workaround. The handler code Imagine you're...

Lambda Durable Functions is a powerful new feature, but its checkpoint + replay model has a few gotchas. Here are five to watch out for. Non-deterministic code The biggest gotcha is when the code is not deterministic. That is, it might do something different during replay. Remember, when a durable execution is replayed, the handler code is executed from the start. So the code must behave exactly the same given the same input. If you use random numbers, or timestamps to make branching...