Comment by revertts

Failures while communicating to the external systems (the kv store and elastic in your example) are usually where this falls down. It's easy to build a system that's consistent ~90% of the time, but if you want to build a system where things like failures during snapshot write or failures during export to elastic are handled properly it starts getting complex (you will need to find ways to recover and retract data, or build smarts into the consumer to query around aborts, or find a way to do a 2PC-esque dance with the external system a la Kafka's transaction support, etc.). Getting to full consistency isn't easy.