In Google Kubernetes Engine (GKE), which object should be used when applications require stable network identities and persistent disks?

When applications require stable network identities and persistent disks in Google Kubernetes Engine (GKE), a StatefulSet is the appropriate choice. StatefulSets are specifically designed for managing stateful applications, allowing them to maintain a unique identity and stable network identity. Each pod in a StatefulSet is assigned a unique ordinal index, which helps in distinguishing them, and this is essential for scenarios where the identity of the application instance matters, such as databases or applications that require consistent storage.

Moreover, StatefulSets enable the use of persistent storage by automatically provisioning a PersistentVolume for each pod. This is critical for applications that need data to persist even when pods are restarted, scaled, or rescheduled. The configuration of StatefulSets ensures that not only is the storage persistent, but the data remains tied to the lifecycle of the respective pods, providing both stability and consistency across the application instances.

In contrast, other options like Deployments and ReplicaSets are more suited for stateless applications, where the instances can be easily recreated and do not require stable identities or persistent storage. A ReplicaController is an earlier iteration of managing replication in Kubernetes with similar capabilities to ReplicaSets, but does not specifically cater to the requirements of network identities or persistent storage in stateful scenarios.