Messaging

In service oriented architecture (including microservices) that leverage messaging, you’re going to run into both types of messages: Commands & Events. What’s the difference between Commands & Events? When should you use a command and when should use an event? YouTube Check out my YouTube channel where I post all kinds of content that accompanies my posts including this video showing everything that is in this post. What’s a Command? Commands are messages with the intent to change the state of the system. They are actions to be performed that have side effects. They may be created by an end-user… Read More »Messaging Commands & Events Explained!

How do you handle business processes and workflows in an asynchronous event-driven architecture? You can use event choreography and orchestration with compensating actions to overcome the lack of distributed transactions or two-phase commits in a distributed system. Here’s how Event Choreography & Orchestration work and examples using NServiceBus. YouTube Check out my YouTube channel where I post all kinds of content that accompanies my posts including this video showing everything that is in this post. Saga Event Choreography Choreography is driven by events from the various services within a system. Each service consumes events, performs an action, and publishes events.… Read More »Event Choreography & Orchestration (Sagas)

“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)