Architecture Patterns with Python

Chapter 11. Event-Driven Architecture: Using Events to Integrate Microservices

In the preceding chapter, we never actually spoke about how we would receive the “batch quantity changed” events, or indeed, how we might notify the outside world about reallocations.

We have a microservice with a web API, but what about other ways of talking to other systems? How will we know if, say, a shipment is delayed or the quantity is amended? How will we tell the warehouse system that an order has been allocated and needs to be sent to a customer?

In this chapter, we’d like to show how the events metaphor can be extended to encompass the way that we handle incoming and outgoing messages from the system. Internally, the core of our application is now a message processor. Let’s follow through on that so it becomes a message processor externally as well. As shown in Figure 11-1, our application will receive events from external sources via an external message bus (we’ll use Redis pub/sub queues as an example) and publish its outputs, in the form of events, back there as well.

Figure 11-1. Our application is a message processor

Tip

The code for this chapter is in the chapter_11_external_events branch on GitHub:

git clone https://github.com/cosmicpython/code.git
cd code
git checkout chapter_11_external_events
# or to code along, checkout the previous chapter:
git checkout chapter_10_commands