Event ordering on Event Bus

[totemcaf]

Hi,

I'm looking at goes, I like a lot several ideas in the implementation.

To gain understanding on it before moving out application to use this framework, I'm doing a proof of concept.

We are using mongodb, so it is ok the backend to store events, and we are evaluating to use Google PubSub as an event bus backend. I'm developing a backend implementation for it.

Doing that task, a question rose my mind and it is regarding the event bus ordering. If using the event bus to publish events for an Aggregate, my questions is if in the design is contemplated the event order for a given aggregate.

I was reading about NATS and see it does not support event ordering (except for events generated in the same source) so if two process instances generate events for the same aggregate (same type and instance) there is chance that subscriber receive events in a different order than version order of the aggregate). Google PubSub support an Ordering Key. Using the Aggregate ID as the ordering key helps to solve this issue.

I'm thinking if that can be solved by the use of a Event Stream in mongodb (I saw you planned to have it), but a more generic solution should be provided.

I'll be glad to read your comments.