Not speaking about their case, but I think some cases a "versioned mutable data store" with a event log that lists updates/inserts makes more sense than an "immutable event log" one like kafka.
Consider the update_order_item_quantity event in a classic event sourced systems. It's not possible to guarantee that two waiters dispatching two such events at same time when current quantity is 1 would not cause the quantity to become negative/invalid.
If the data store allowed for mutability and produced an event log it's easy:
Instead of dispatching the update_order_item_quantity you would update the order document specifying the current version. In the previous example second request would fail since it specified a stale version_id. And you can get the auditability benefits of classic event sourcing system as well because you have versions and an event log.
This kind of architecture is trivial to implement with CouchDB and easier to maintain than kafka. Pity it's impossible to find managed hosting for CouchDB outside of IBM.
Consider the update_order_item_quantity event in a classic event sourced systems. It's not possible to guarantee that two waiters dispatching two such events at same time when current quantity is 1 would not cause the quantity to become negative/invalid.
If the data store allowed for mutability and produced an event log it's easy:
Instead of dispatching the update_order_item_quantity you would update the order document specifying the current version. In the previous example second request would fail since it specified a stale version_id. And you can get the auditability benefits of classic event sourcing system as well because you have versions and an event log.
This kind of architecture is trivial to implement with CouchDB and easier to maintain than kafka. Pity it's impossible to find managed hosting for CouchDB outside of IBM.