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Kubernetes Questions and Answers

Kubernetes 101

Q) What are the features of Kubernetes?

k8s-features

Q) How is Kubernetes different from Docker Swarm?
  • Docker Swarm is Docker’s native, open-source container orchestration platform that is used to cluster and schedule Docker containers.
  • Docker Swarm is more convenient to set up but doesn’t have a robust cluster, while Kubernetes is more complicated to set up but benefits from a more robust cluster.
  • Docker Swarm can’t do auto-scaling; Kubernetes can.
  • Docker Swarm is faster in scaling but lacks features like GUI, auto-rollbacks, and native monitoring/logging tools that Kubernetes has.
  • Kubernetes supports automatic rollbacks; Docker Swarm does not.
Q) How are Kubernetes & Docker related?
  • Docker is a containerization platform.
  • Kubernetes orchestrates and manages Docker containers at scale.
Q) What is the difference between deploying applications on hosts & containers?
  • hosts-containers
  • Host-based apps share OS libraries.
  • Container-based apps are isolated with only shared kernel.
Q) What is Container Orchestration?
  • It refers to managing multiple containers as one system.
  • It ensures communication, deployment, scaling, and availability of microservices spread across containers.
Q) How does Kubernetes simplify containerized Deployment?
  • Kubernetes abstracts infrastructure complexity.
  • Provides auto-scaling, self-healing, load balancing, and monitoring.
  • It is cloud-agnostic.
Q) What do you know about clusters in Kubernetes?
  • k8s-cluster
  • A Kubernetes cluster has master (API, scheduler) and worker nodes (Kubelet, pods).
  • Desired state is managed via deployment files submitted to the API.
Q) What is a Pod in Kubernetes?
  • A pod is the smallest deployable unit in Kubernetes.
  • It can contain one or more containers. 
    kubectl get pods -n <namespace-name>
Q) What is Kubectl?
  • CLI to interact with Kubernetes API.
  • Used to deploy apps, inspect resources, and troubleshoot.
Q) What is Kubelet?
  • An agent that runs on each node in the cluster.
  • Ensures the containers described in PodSpecs are running.
Q) What is etcd?
  • A distributed key-value store used by Kubernetes.
  • Stores configuration data and state of the cluster.
Q) What are the different services within Kubernetes?
  • k8s-services
Q) What is the role of a pod?
  • Pods encapsulate containers and provide shared storage, IP, and communication.
Q) What is the LoadBalancer in Kubernetes?
  • Used to expose services externally.
  • Internal LB balances traffic inside the cluster.
  • External LB routes external traffic to the services.

ARCHITECTURE BASED QUESTIONS

Q) What are the different components of Kubernetes Architecture?
  • Kubernetes architecture is composed of two major components:
  • Master Node

  • Worker Node

  • Master Node Components:

  • kube-apiserver: Handles communication within the cluster.
  • kube-scheduler: Assigns pods to available worker nodes.
  • kube-controller-manager: Maintains the cluster’s desired state.

  • etcd: Key-value store for all cluster data.

  • Worker Node Components:

  • kubelet: Ensures containers are running as specified.

  • kube-proxy: Manages networking and communication for pods.

  • k8s-arch

  • kubernetes-architecture
Q) What are the various K8 related services running on nodes and role of each service?
  • Kubernetes cluster consists of two node types:
  • Master Nodes

  • Executor (Worker) Nodes (also runs on Master)

  • Master Node Services:

  • kube-apiserver: Entry point for the Kubernetes cluster (API gateway).
  • kube-scheduler: Assigns pods to nodes based on available resources.

  • kube-controller-manager: Monitors cluster state and attempts to maintain desired configuration.

  • Executor Node Services:

  • kube-proxy: Network proxy handling TCP, UDP, and SCTP forwarding.
  • kubelet: Ensures pods are running and in healthy state per spec from kube-apiserver.

Technical QUESTIONS

Q) What is the difference between ConfigMap and Secret? (With examples)
  • ConfigMap: Stores non-sensitive configuration data in plain text format.
  • Secret: Stores sensitive information (e.g., passwords) in base64-encoded format.

ConfigMap Example: 

kubectl create configmap myconfigmap --from-literal=env=dev

Secret Example: 

echo -n 'admin' > ./username.txt
echo -n 'abcd1234' > ./password.txt
kubectl create secret generic mysecret --from-file=./username.txt --from-file=./password.txt

ConfigMap vs Secret

Q) How to use secrets in Kubernetes?
  • Secrets are Kubernetes objects used to store encrypted sensitive data such as usernames and passwords.

Secret YAML Example: 

apiVersion: v1
kind: Secret
metadata:
  name: tomcat-pass
type: Opaque
data:
  password: <User Password>
  username: <User Name>

Create Secret: 

kubectl create -f Secret.yaml
kubectl apply -k .
Q) How to control the resource usage of a POD?

  • Use requests and limits in the container spec.

  • request: Minimum amount of resources guaranteed.

  • limit: Maximum resource usage allowed. Exceeding this may lead to throttling or termination.

Example in Pod spec: 

resources:
  requests:
    cpu: "250m"
    memory: "64Mi"
  limits:
    cpu: "500m"
    memory: "128Mi"
Q) Recommended way of managing the access to multiple clusters?
  • Use the Kubernetes config file (usually located at ~/.kube/config) to store access information for multiple clusters.
  • Use kubectl config subcommands to switch between and manage clusters.

Examples: 

kubectl config use-context my-cluster
kubectl config get-contexts
Q) What is PDB (Pod Disruption Budget)?

  • A Pod Disruption Budget (PDB) ensures a minimum number of pods remain available during voluntary disruptions (e.g., node upgrade).

  • Example:

  • Deployment has 5 replicas.
  • PDB allows 1 pod disruption at a time, meaning at least 4 pods must remain available.
Q) How to troubleshoot if the POD is not getting scheduled?
  • Common causes: Insufficient resources, node selectors, taints, etc.

  • Use the following commands: 

    kubectl describe pod <pod-name> -n <namespace>
kubectl get events

  • Look for events such as FailedScheduling or resource-related errors.

Q) What are taints and tolerations?
  • Taints: Set on nodes to prevent certain pods from being scheduled unless they tolerate the taint.

  • Tolerations: Allow pods to be scheduled on nodes with matching taints.

  • Useful for workload isolation or reserving nodes for specific teams or services.

Example Taint: 

kubectl taint nodes node1 key=value:NoSchedule

Matching Toleration in Pod: 

tolerations:
- key: "key"
  operator: "Equal"
  value: "value"
  effect: "NoSchedule"