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...

Two weeks ago, I gave you the biggest serverless announcements pre-re:Invent (see here). So here are the biggest serverless announcements during re:Invent 2025. Lambda Managed Instances Here’s the official announcement. A common pushback against Lambda is that “it’s expensive at scale” because: 1) Each execution environment can only process one request at a time, wasting available CPU cycles while you wait for IO response. 2) Paying for execution time is less efficient when handling thousands...

Like London buses, we've waited years for true innovations to the Lambda platform and two came at the same time! Lambda Managed Instances Lambda Durable Functions I will be updating the Production-Ready Serverless workshop to cover these new features in the January cohort. For now, let's take a closer look at Lambda Managed Instances, why you should care and when to use it. Introducing Lambda Managed Instances A common pushback against Lambda is that "it's expensive at scale" because: 1) Each...