The data in a **StatefulSet does not get replicated across nodes by Kubernetes itself**. This is a common point of confusion. The StatefulSet's job is to ensure that each pod has a unique, stable identity and that its associated storage is persistent and unique to that pod.
To achieve data replication, you need to use a separate, application-specific mechanism, such as:
* **Database-level Replication:** For databases like MySQL or PostgreSQL, you configure them to replicate data from a primary instance to one or more secondary instances.
* **Distributed File Systems:** Using a system like Ceph or GlusterFS, which handles the data replication and synchronization across multiple storage nodes.
* **Cloud Provider Features:** Many cloud-native databases offer built-in replication and high-availability features.
In your diagram, the pods would all be configured to use a remote volume for their database, but the **database application itself**, running inside the pods, would be responsible for synchronizing data between the instances. The StatefulSet simply ensures that each pod can reliably find and attach to its correct persistent volume, even if it's restarted on a different node.
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