Interview › Kubernetes, Docker, Helm & Podman
What is the difference between the HPA, VPA, and Cluster Autoscaler?
Kubernetes, Docker, Helm & Podman · Basic level
Answer
HPA scales Pod replicas, VPA adjusts resource requests for Pods, and Cluster Autoscaler changes node count. They solve different layers of capacity: workload replicas, per-Pod sizing, and cluster infrastructure capacity.
Technical explanation
HPA and VPA can conflict if both change CPU/memory for the same workload without a careful mode.
Cluster Autoscaler reacts after Pods are unschedulable, so HPA can create demand before nodes exist.
Kubernetes workload controllers encode different lifecycle guarantees: interchangeable replicas, stable identities, node-local agents, or finite tasks.
Storage decisions must align with durability, access mode, zone placement, backup, restore, and failover behavior.
Autoscaling should be designed with metrics, scheduling constraints, PDBs, and node capacity together.
Hands-on example
1. Deploy a workload for this exercise using kubectl apply and a small test image such as nginx, busybox, or a purpose-built app: compare HPA replica scaling, VPA recommendations, and Cluster Autoscaler node behavior.
2. Inspect ownerReferences, events, Pods, PVCs, PVs, EndpointSlices, and metrics depending on the resource being tested.
3. Create a realistic disruption: delete a Pod, scale replicas, restart a node, fill a queue, or recreate storage attachment in a test environment.
4. Write the runbook entry covering expected behavior, safe rollback, and what alarms should exist.
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- Explain the Kubernetes control plane components (API server, etcd, scheduler, controller manager).
- What runs on a worker node (kubelet, kube-proxy, container runtime)?
- What is a Pod, and why does Kubernetes schedule Pods rather than containers?
- What is the difference between a Pod, a ReplicaSet, and a Deployment?
- How does a Deployment perform a rolling update, and how do maxSurge and maxUnavailable work?
- How do you roll back a Deployment, and how does Kubernetes track revisions?
- What is a Service, and what are the types (ClusterIP, NodePort, LoadBalancer, ExternalName)?