Top 10 Kubernetes Interview Questions for Spring Boot Deployment

Kubernetes (commonly abbreviated as K8s) has become the backbone of many microservices deployments, transforming how applications are managed and scaled. For Spring Boot developers, Kubernetes offers opportunities to seamlessly deploy, scale, and maintain robust applications in production environments.

This blog covers the Top 10 Kubernetes interview questions specific to deploying Spring Boot applications, tailored to help you gain an edge during interviews. With practical examples and clear explanations, you’ll get everything you need to know to ace your Kubernetes-related discussions.

What is Kubernetes and Why is It Used?
What Are Pods, Deployments, and Services?
How Does K8s Handle Scaling and Autoscaling?
What is a ConfigMap vs Secret?
Readiness and Liveness Probes
How Do You Deploy a Spring Boot App to K8s?
Difference Between StatefulSet and Deployment
Rolling Updates and Rollback
Helm and Its Use in Deployments
Kubernetes Logging and Monitoring Integration
FAQs

1. What is Kubernetes and Why is It Used?

Kubernetes is an open-source container orchestration platform that automates deploying, managing, and scaling applications. It simplifies complexities like high availability, resource optimization, load balancing, and infrastructure abstraction.

Why Use Kubernetes?

Scalability: Automatically adjusts workloads based on demand.
Resilience: Restarts failed containers and ensures application uptime.
Portability: Runs anywhere—on-premises, public cloud, or hybrid environments.
Service Discovery: Finds and manages application instances efficiently.

Use Case: Imagine running a Spring Boot application with multiple services. Kubernetes simplifies cross-service communication and scales services dynamically as traffic increases.

2. What Are Pods, Deployments, and Services?

Understanding Kubernetes building blocks is critical for deploying applications.

Pods

Definition: The smallest deployable unit in Kubernetes, encapsulating containers along with storage and networking settings.
Use Case: Each Spring Boot app instance runs in a pod.

Deployments

Definition: Higher-level abstraction for managing pods, enabling updates, scaling, and rollbacks.
Use Case: Deployments manage multiple replicas of a Spring Boot app, ensuring high availability.

Services

Definition: Kubernetes services expose pods to internal or external networks for communication.
Use Case: Spring Boot services like REST APIs are exposed as services for client access.

3. How Does K8s Handle Scaling and Autoscaling?

Horizontal Pod Autoscaler (HPA)

The HPA adjusts the number of pod replicas based on CPU or custom metrics like memory or request latency.

Manual Scaling Example

Manually scale a deployment with this command:

   kubectl scale --replicas=4 deployment/spring-boot-app

Autoscaling Example

Define an HPA for automatic scaling:

   apiVersion: autoscaling/v2
   kind: HorizontalPodAutoscaler
   spec:
     scaleTargetRef:
       apiVersion: apps/v1
       kind: Deployment
       name: spring-boot-app
     minReplicas: 2
     maxReplicas: 10
     metrics:
       - type: Resource
         resource:
           name: cpu
           target:
             type: Utilization
             averageUtilization: 70
   ```  

Scaling ensures efficient resource utilization, especially in traffic spikes.  

---  

## 4. What is a ConfigMap vs Secret?  

### ConfigMap  
Stores non-sensitive configuration data as key-value pairs.  
**Use Case:** Externalizing a Spring profile (e.g., `application.properties`) using a ConfigMap.  

### Secret  
Stores sensitive data such as passwords and API keys in Base64 encoding.  
**Use Case:** Storing database credentials securely for Spring Boot apps.  

Example for creating both resources via CLI:
   ```bash
   kubectl create configmap app-config --from-literal=profile=dev
   kubectl create secret generic db-credentials --from-literal=username=admin --from-literal=password=secret123

5. Readiness and Liveness Probes

Kubernetes uses probes to monitor an application’s health.

Liveness Probe

Checks if the app is alive and restarts the container if it isn’t.

Example:

   livenessProbe:
     httpGet:
       path: /health
       port: 8080
     initialDelaySeconds: 5
     periodSeconds: 10

Readiness Probe

Checks if the app is ready to start handling traffic.

Example:

   readinessProbe:
     httpGet:
       path: /ready
       port: 8080
     initialDelaySeconds: 5
     periodSeconds: 10

6. How Do You Deploy a Spring Boot App to K8s?

Steps:

Build a Docker Image:

Use a Dockerfile to containerize your app.

   FROM openjdk:17-jdk-slim
   COPY target/app.jar app.jar
   ENTRYPOINT ["java", "-jar", "/app.jar"]
   ```  

2. **Push Image to Repository:**  
   ```bash
   docker push <your-repo>/spring-boot-app

Create a Deployment YAML:

   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: spring-boot-app
   spec:
     replicas: 3
     selector:
       matchLabels:
         app: spring-boot-app
     template:
       metadata:
         labels:
           app: spring-boot-app
       spec:
         containers:
         - name: spring-boot-app
           image: <your-repo>/spring-boot-app
           ports:
           - containerPort: 8080

Deploy to Kubernetes:

   kubectl apply -f deployment.yaml

7. Difference Between StatefulSet and Deployment

Deployment

Manages stateless apps.
Pods can be replaced without retaining their identity.

StatefulSet

Manages stateful apps with sticky identities for pods.
Common for databases and systems requiring persistent storage.

Example: A MySQL cluster uses StatefulSet, whereas a Spring Boot microservice uses a Deployment.

8. Rolling Updates and Rollback

Rolling Updates

Incrementally replaces old pods with new ones without downtime.

Execute with:

   kubectl set image deployment/spring-boot-app app=<new-image>

Rollback

Rollback to the previous version if something goes wrong:

   kubectl rollout undo deployment/spring-boot-app

9. Helm and Its Use in Deployments

Helm, a Kubernetes package manager, simplifies application deployment.

Why Use Helm?

Reusability with templated Helm Charts.
Version-controlled deployments.

Example: Deploy a Spring Boot app using Helm:

   helm install springboot-app ./my-helm-chart

10. Kubernetes Logging and Monitoring Integration

Logging

Centralized logging with tools like Elasticsearch, Fluentd, and Kibana (EFK stack).

Monitoring

Monitor metrics with Prometheus and visualize them using Grafana dashboards.

Example: Deploy a Prometheus stack to observe Spring Boot performance metrics in real time.

FAQs

How does Kubernetes improve Spring Boot app deployment?

It automates scaling, rolling updates, and monitoring, reducing operational complexity.

Can I use Kubernetes without prior Docker experience?

While Docker is commonly used, Kubernetes supports container runtimes like CRI-O and containerd. Learning Docker gives you foundational knowledge for Kubernetes.

Why are StatefulSets necessary for databases?

They ensure predictable pod ordering and persistent volumes, critical for databases.

Summary

Kubernetes, with its rich feature set, enhances the deployment, scalability, and monitoring of Spring Boot applications. From understanding core concepts like ConfigMaps, Secrets, and probes to leveraging tools like Helm and Prometheus, mastering Kubernetes will make you an invaluable asset to DevOps and development teams alike.

By preparing for questions related to Spring Boot deployments on Kubernetes, you’ll not only impress interviewers but also elevate your expertise in real-world application deployment scenarios.

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