I'm a Korean DevOps engineer preparing for international opportunities. Since English isn’t my first language, I’ve been practicing both my language skills and technical knowledge at the same time.
As part of my daily English practice, I asked ChatGPT (acting as my senior DevOps engineer) to give me one interview-style question each day. I try to answer in English based on what I know, and then improve my explanation through feedback and correction.
Here’s today’s question and my answer:
Question
What happens when you scale a StatefulSet from 2 replicas to 3?
My First Answer (Raw)
When you scale out statefulset's replicas from 2 to 3, a new pod is generated with index 2. statefulset manages pods the way it can distinguish each pod by it's name and index, a newly populated pod has expectable name.
you can access the pod with the address like 'pod name.namespace.svc cluster.local' which is offered by headless service, and this is how it can be uniquely identifiable and accesable in a cluster.
Also, if volumeclaimtemplates are defined, a pvc is generated with a new pod.
If the storage class supports dynamic provisioning, condition matching pv is automatically made and bound to the pvc. If condition matching pv already exists, it could be bound.
the pvc is uniquley linked to the pod's name so that data can be persistent even if a pod is removed and regenerated. This ensure statefulset can maintain data persistency and pod's uniqueness.
Refined Answer (with feedback)
When you scale a StatefulSet from 2 to 3 replicas, a new pod with the index 2 is created.
StatefulSet manages pods in a way that each one is uniquely identifiable by its name and index, so the newly created pod gets a predictable name.
You can access this pod using a DNS address like pod-name.namespace.svc.cluster.local, which is provided by a headless service.
This allows the pod to be uniquely addressable within the cluster.
If volumeClaimTemplates are defined, a new PVC is automatically created for the new pod.
If the associated StorageClass supports dynamic provisioning, a new PV that matches the claim’s requirements will be provisioned and bound automatically.
If a matching PV already exists, it will be used instead.
Since the PVC is uniquely associated with the pod’s name, the pod can reconnect to the same volume even after it is deleted and recreated.
This ensures data persistence and stable identity, which are key characteristics of StatefulSets.
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