Apache Kafka is a scalable streaming platform with built-in dynamic client scaling. The elastic scale-in/scale-out feature leverages Kafka’s “rebalance protocol” that was designed in the 0.9 release and improved ever since then. The original design aims for on-prem deployments of stateless clients. However, it does not always align with modern deployment tools like Kubernetes and stateful stream processing clients, like Kafka Streams. Those shortcoming lead to two mayor recent improvement proposals, namely static group membership and incremental rebalancing (which will hopefully be available in version 2.3). This talk provides a deep dive into the details of the rebalance protocol, starting from its original design in version 0.9 up to the latest improvements and future work. We discuss internal technical details, pros and cons of the existing approaches, and explain how you configure your client correctly for your use case. Additionally, we discuss configuration tradeoffs for stateless, stateful, on-prem, and containerized deployments.