Although Pact supports testing of messages, I find that the recommended flow in the "Pact Nirvana" doesn't quite match the flow that I understand an Event Driven Application needs.
Let's say we have an Order management service and a Shipping management service.
The Shipping service emits ShippingPreparedEvents that are received by the Order service.
If we deleted a field inside the ShippingPreparedEvent, I'd expect first to make a change to the Order service so that it stops reading the old field. Deploy it. And then make the change in the Shipping service and deploy it.
That way, there wouldn't have any downtime on the services.
However, I believe Pact would expect to deploy the Shipping service first (it's the provider of the event) so that the contract can be verified before deploying the consumer. In this case, deploying the provider first will break my consumer.
Can this situation be avoided somehow? Am I missing anything?
Just to provide more context, we can see in this link that different changes would require different order of deployment. https://docs.confluent.io/current/schema-registry/avro.html#summary I won't be using Kafka nor Avro, but I believe my flow would be similar.
Thanks a lot.
If we deleted a field inside the ShippingPreparedEvent, I'd expect first to make a change to the Order service so that it stops reading the old field. Deploy it. And then make the change in the Shipping service and deploy it. That way, there wouldn't have any downtime on the services.
I agree. What specifically in the Pact Nirvana guide gives you the impression this isn't the way to go? Pact (and the Pact Broker) don't actually care about the order of deployments.
In your case, removing the field would cause a failure of a can-i-deploy check, because removing the field would break the Order Management Service. The only approach would be to remove the field usage from the consumer, publish a new version of that contract and deploy to Production first.