Derek Comartin

“At Least Once” message guarantees that a message will be delivered to a consumer once or many times. This means that you need to develop your consumers to be able to effectively handle duplicate messages. The term for this is having idempotent consumers. Not doing so could result in some bad outcomes for your system. For example, processing a message twice that creates an order, could create two orders. That would not likely be a good outcome. Why do messages get delivered more than once? How do you handle duplicates? Here’s how to make idempotent consumers and be resilient to… Read More »Handling Duplicate Messages (Idempotent Consumers)

What’s the Outbox Pattern? A reliable way of saving state to your database and publishing a message/event to a message broker. Why do you need it? When you get into messaging, you will often find code that needs to save state to your database, and then publish a message/event to a message broker. Unfortunately, because they are two different resources, you need a distributed transaction to make these atomic. There is another option to use the Outbox Pattern which does not require a distributed transaction and most messaging libraries support it. YouTube Check out my YouTube channel where I post… Read More »Outbox Pattern: Reliably Save State & Publish Events