Lambda Durable Functions makes it easy to implement business workflows using plain Lambda functions. Besides the intended use cases, they also let us implement ETL jobs without needing recursions or Step Functions. Many long-running ETL jobs have a time-consuming, sequential steps that cannot be easily parallelised. For example: Fetching data from shared databases/APIs with throughput limits. When data needs to be processed sequentially. Historically, Lambda was not a good fit for these...

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...