This is a tutorial on building event-driven application in Golang using Watermill, a fantastic Go library for working efficiently with message streams.
We run a publisher in the background, publishing messages to the message broker on topic incoming_topic every 3 seconds. At the same time, helloHandler and incomingTopicHandler subscribe on topic incoming_topic; outgoingTopicHandler subscribes on outgoing_topic. Once helloHandler receives a message, it will then publish another greeting message to topic outgoing_topic, which will be recived by outgoingTopicHandler.
In transport.go, we decouple our service logics from the broker implementation. That is, we are able to switch to any message broker without changing existing code as long as the broker client implements message.Publisher and message.Subscriber interface.
docker-compose upWe can switch to GoChannel Pub/Sub by simply setting WATERMILL_PUBSUB_TYPE to empty string.