Practical Microservices

Thinking Through the Expected Flow

We know what’s supposed to happen when someone registers. The register-users application writes a Register command that the identity component picks up. It writes a Registered event in response to that command. It then handles its own Registered event by writing a Send command that send-email observes and handles by sending the email and writing a Sent event. identity is listening for that Sent event. How can we construct a view that tells us if these three things happened and in the proper sequence? Is there a piece of data we have that links these messages across time and component boundaries, also known as distributed tracing?

Sure is. Remember those traceIds we’ve been so careful to include? All three ...