Docker Interview Questions:
1).🔥 Docker Interview Questions (5+ Years Experience)
1. What is the difference between Docker Image and Container?
Answer:
* Image → Blueprint (read-only template)
* Container → Running instance of image
👉 Example:
docker build -t myapp .
docker run -d myapp
2. Explain Docker Architecture
Answer:
* Docker Client
* Docker Daemon (dockerd)
* Docker Registry (Docker Hub / ECR)
* Docker Objects (Images, Containers, Networks, Volumes)
👉 Check:
docker info
3. What happens when you run docker run?
Answer (Important):
1. Check image locally
2. Pull from registry if not present
3. Create container
4. Setup filesystem (UnionFS)
5. Allocate network
6. Start process
4. Difference: CMD vs ENTRYPOINT
Answer:
* CMD → Default command (can override)
* ENTRYPOINT → Fixed command
👉 Example:
CMD ["echo", "Hello"]
ENTRYPOINT ["echo"]
5. Multi-stage build – Why?
Answer:
* Reduce image size
* Remove build dependencies
👉 Example:
FROM node:18 AS build
WORKDIR /app
COPY . .
RUN npm install && npm run build
FROM nginx:alpine
COPY --from=build /app/build /usr/share/nginx/html
6. How do you reduce Docker image size?
Answer:
* Use Alpine base image
* Multi-stage builds
* Remove cache
👉 Example:
RUN apt-get update && apt-get install -y curl && rm -rf /var/lib/apt/lists/*
7. Difference between COPY and ADD
Answer:
* COPY → Simple file copy
* ADD → Supports URL + tar extraction
👉 Best Practice: Use COPY unless needed
8. What is Docker Volume?
Answer:
* Persistent storage outside container
👉 Example:
docker volume create mydata
docker run -v mydata:/data nginx
9. Bind Mount vs Volume
Answer:
* Bind Mount → Host path
* Volume → Managed by Docker
10. Explain Docker Networking Types
Answer:
* bridge (default)
* host
* none
* overlay (for Swarm/K8s)
👉 Check:
docker network ls
11. How containers communicate?
Answer:
* Same network → via container name (DNS)
12. What is Docker Compose?
Answer:
* Multi-container management tool
👉 Example:
version: '3'
services:
web:
image: nginx
db:
image: mysql
👉 Run:
docker-compose up -d
13. What is Dockerfile best practice?
Answer:
* Use minimal base images
* Order layers properly
* Avoid root user
14. What is .dockerignore?
Answer:
* Ignore unnecessary files
👉 Example:
node_modules
.git
15. How to debug a container?
Answer:
👉 Logs:
docker logs container_id
👉 Exec:
docker exec -it container_id /bin/bash
16. Container is not starting – what will you do? (Scenario)
Answer:
1. Check logs
2. Check port conflicts
3. Check CMD/ENTRYPOINT
4. Check resource limits
17. Difference: Detached vs Interactive mode
docker run -d nginx
docker run -it ubuntu
18. How do you expose ports?
docker run -p 8080:80 nginx
19. What is Docker Registry?
Answer:
* Storage for images
Examples:
* Docker Hub
* AWS ECR
20. How to push image?
docker tag myapp username/myapp
docker push username/myapp
21. What is container lifecycle?
* Created
* Running
* Paused
* Stopped
* Removed
22. Resource limits in Docker?
docker run -m 512m --cpus=1 nginx
23. What is Docker Swarm?
Answer:
* Native clustering tool
24. Difference between Docker and Kubernetes?
Answer:
* Docker → Container runtime
* Kubernetes → Orchestration
25. Real-time Scenario 🔥
Problem:
Container works locally but fails in server.
Answer approach:
* Check environment variables
* Check ports
* Check network/security group
* Check image version mismatch
26. What is health check?
HEALTHCHECK CMD curl --fail http://localhost || exit 1
27. How to handle secrets?
Answer:
* Use Docker secrets / env variables
* Avoid hardcoding
28. How to clean unused resources?
docker system prune -a
29. What is Layer caching?
Answer:
* Docker caches each step → faster builds
30. Explain real-time CI/CD Docker usage
Answer:
* Build image → push to registry → deploy via Kubernetes
====================
Kubernestes Interview questions:
==========================
🔥 DevOps Scenario-Based Interview (5+ Years)
1. 🚨 Deployment failed in production — what will you do?
Answer approach (very important):
* Check pipeline logs
* Identify failure stage (Build / Deploy)
* Rollback if critical
👉 Commands:
kubectl rollout undo deployment my-app
kubectl get pods
kubectl logs pod-name
👉 Pro Answer Line:
“First I ensure service availability by rollback, then I debug root cause.”
2. 🚨 Application is slow — how do you troubleshoot?
Answer:
* Check CPU/Memory
* Check DB latency
* Check network
👉 Commands:
top
kubectl top pod
kubectl describe pod pod-name
👉 Tools:
* Prometheus
* Grafana
* CloudWatch
3. 🚨 Pod is in CrashLoopBackOff
Answer:
* Check logs
* Check env variables
* Check config issues
kubectl logs pod-name
kubectl describe pod pod-name
4. 🚨 Website not accessible
Answer:
* Check Service
* Check Ingress
* Check DNS
kubectl get svc
kubectl get ingress
kubectl get endpoints
5. 🚨 Docker container not starting
Answer:
* Check logs
* Check CMD/ENTRYPOINT
* Check port conflict
docker logs container_id
docker inspect container_id
6. 🚨 High CPU usage in server
Answer:
* Identify process
* Kill or scale
top
ps -ef | grep java
7. 🚨 Disk space full
Answer:
df -h
du -sh *
👉 Fix:
* Clean logs
* Remove unused Docker images
docker system prune -a
8. 🚨 CI/CD pipeline is failing
Answer:
* Check pipeline logs
* Validate credentials
* Check syntax
👉 Example (Jenkins):
* Check console output
* Re-run stage
9. 🚨 Terraform apply failed
Answer:
terraform validate
terraform plan
terraform apply
👉 Debug:
* State file issues
* Resource conflict
10. 🚨 Infrastructure drift detected
Answer:
terraform plan
👉 Fix:
* Re-apply or import resource
11. 🚨 LoadBalancer not working
Answer:
* Check security group
* Check target health
kubectl get svc
kubectl describe svc
12. 🚨 Application logs not visible
Answer:
kubectl logs pod-name
docker logs container_id
👉 Check:
* Logging config
* Sidecar (Fluentd)
13. 🚨 Secrets exposed in code
Answer:
* Move to:
* Kubernetes Secrets
* AWS Secrets Manager
14. 🚨 Multiple environments (Dev, QA, Prod) — how manage?
Answer:
* Use:
* Separate namespaces
* Separate pipelines
* Terraform workspaces
15. 🚨 Zero downtime deployment — how?
Answer:
* Rolling updates
* Blue-Green
* Canary
kubectl rollout status deployment my-app
16. 🚨 Pod cannot connect to DB
Answer:
* Check network
* Check credentials
* Check service name
kubectl exec -it pod-name -- ping db-service
17. 🚨 API returning 500 error
Answer:
* Check logs
* Check backend service
* Check DB
18. 🚨 Kubernetes node NotReady
Answer:
kubectl get nodes
kubectl describe node node-name
👉 Check:
* kubelet
* disk/memory
19. 🚨 SSL not working
Answer:
* Check certificate
* Check Ingress
20. 🚨 Autoscaling not working
Answer:
kubectl get hpa
kubectl describe hpa
👉 Check:
* metrics-server
21. 🚨 Memory leak in app
Answer:
* Monitor usage
* Restart pods
* Fix code
22. 🚨 Network issue between services
Answer:
kubectl exec -it pod -- curl service-name
23. 🚨 Version rollback required
kubectl rollout undo deployment
24. 🚨 Git conflict in pipeline
Answer:
* Resolve locally
* Push again
25. 🚨 Monitoring alerts triggered
Answer:
* Check metrics
* Identify spike
* Take action
💥 Real Interview Question (Very Important)
👉 “Explain a production issue you handled”
Perfect Answer Structure:
1. Problem
2. Impact
3. Action
4. Result
👉 Example:
“We faced high latency in production. I checked metrics in Prometheus, identified high CPU usage, scaled pods using HPA, and resolved the issue with zero downtime.”
Linux interview Questions :
1).How to recover accidently deleted /etc/fstab into linux os ? anyone deleted this /etc/fstab .after this we can' boot ur os. boot into recovery mode . then go to the linux terminal page . here we have to execute the blkid command here it will list out the avilble partions and attached filesystems . if your deleting the /etc/fatab.that time root parttion won't be work now we can mount the root parttion in rw mode mount -t ext4 -0 rw,remount dev/sda1 / 2).VMSTAT command into linux ? 3).iostat and dstat command into linux os ? 4).LInux free command into linux os ? in this way we can check it our the memeory usage and swap memeory as well. then it will display out the , used,space avilble ,total ,buffer/catche abd shared what is free space we can execute the command like as the, free -b command : we will get the particular output for the bits so if you want to getto int the outpit in kilobytes : so we can execut ethe comamnd like as the, free -k free -g: it will sh...
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