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A real-world use case of StatefulSets in Kubernetes is deploying a highly available database or distributed system that requires stable network identities, persistent storage, and ordered deployment, such as:

Use Case: Deploying a MongoDB Replica Set
Scenario:
You want to deploy a MongoDB replica set in Kubernetes with 3 nodes: Primary, Secondary, and Arbiter.

Why StatefulSet?

  1. Stable Hostnames:
    MongoDB replica members need predictable hostnames (e.g., mongo-0, mongo-1, mongo-2) to form a cluster.

  2. Persistent Storage:
    Each pod requires its own persistent volume to store data. StatefulSet ensures the volume is "sticky" to the pod even after rescheduling.

  3. Ordered Start/Stop:
    MongoDB needs initialization in a specific order (e.g., primary before secondaries), which StatefulSets support.

  4. Scaling and Rolling Updates:
    StatefulSets help you scale replica sets while keeping identity and storage consistent.

Other Real-World Examples:
Kafka:
Brokers require stable identities and persistent logs.

Zookeeper:
Needs stable network IDs and ordered startup for leader election.

Elasticsearch:
Master and data nodes benefit from sticky storage and identity.

Redis Cluster Mode:
Shards and replication nodes require predictable addresses and durable volumes.

Venkat C S