For readers of this question, it is important to tell them you are mostly using Kafka as the Event Bus within the Axon application entirely.
Application publish on the Axon.Kafka topic and read back from it, without any direct relation to the RDBMS Event Store underneath it.
This makes it so that you are using a SimpleEventBus internally, not the EmbeddedEventStore/AxonServer implementations.
Any how, regarding your buffer question, no there are none.
Added, it feels like you are not sure where the event “drops” between event publication and having the KafkaProducer publish it to the Axon.Events topic.
Firstly, I would start trying to figure out where it is dropped and for that I think adding monitoring is the first step; otherwise everybody is just guessing.
To that end the MessageMonitors Axon provides would be suitable as a first stab, I think.
You can either use DropWizard Metrics or Micrometer as the implementation of metrics.
Added, the KafkaPublisher also allows the addition of a MessageMonitor through the Builder.
This monitor is not auto configured for you at the moment, due to the extension’s RC state.
Let us know, after some further monitoring, where you see the message being dropped within the framework.
If it’s not within the framework, I would have a look at the Kafka set up you are using.
Hope this’ll bring you the specific issue!
And, if it is an issue, I’d like to ask you to add it as such here.
Steven van Beelen
Axon Framework Lead Developer