DevOps Interview Questions¶

🎯 Learning Objectives

Master 200+ DevOps interview questions
Understand detailed answers with examples
Practice explaining complex concepts
Prepare for technical and behavioral rounds

This chapter contains 200+ DevOps interview questions with detailed answers. Practice these to ace your interviews!

How to Use This Chapter

Read questions and try to answer before looking at solutions
Practice explaining answers out loud
Focus on understanding, not memorization
Use STAR method for behavioral questions

Linux & System Administration¶

Q1: Explain the difference between `kill`, `killall`, and `pkill`¶

Answer: - kill: Requires PID, sends signal to specific process

kill -9 1234

- killall: Uses process name, kills all matching processes

killall nginx

- pkill: Pattern-based, more flexible

pkill -f "python script.py"

Q2: What is the difference between `restart` and `reload` for services?¶

Answer: - Restart: Stops service completely, then starts it (downtime) - Reload: Applies new configuration without stopping service (no downtime) - Use reload when possible to avoid service interruption

Q3: How do you find files larger than 100MB?¶

Answer:

find / -type f -size +100M 2>/dev/null
find / -type f -size +100M -exec ls -lh {} \;

Q4: Explain file permissions 755¶

Answer: - 7 (owner): Read(4) + Write(2) + Execute(1) = rwx - 5 (group): Read(4) + Execute(1) = r-x - 5 (others): Read(4) + Execute(1) = r-x

Docker¶

Q5: What is the difference between Docker image and container?¶

Answer: - Image: Read-only template, like a class in programming - Container: Running instance of an image, like an object - Image is static, container is dynamic

Q6: Explain Docker layers¶

Answer: - Docker images are built in layers - Each Dockerfile instruction creates a layer - Layers are cached for faster builds - Layers are read-only, containers add writable layer on top

Q7: How do you reduce Docker image size?¶

Answer: 1. Use multi-stage builds 2. Use Alpine or slim base images 3. Combine RUN commands to reduce layers 4. Use .dockerignore to exclude unnecessary files 5. Remove package managers and build tools in final stage

Q8: What is the difference between `CMD` and `ENTRYPOINT`?¶

Answer: - CMD: Default command, can be overridden - ENTRYPOINT: Always executed, arguments appended - Use ENTRYPOINT for fixed commands, CMD for defaults

Kubernetes¶

Q9: Explain Kubernetes architecture¶

Answer: - Master Node: Control plane (API server, etcd, scheduler, controller manager) - Worker Nodes: Run pods (kubelet, kube-proxy, container runtime) - Pods: Smallest deployable unit - Services: Network abstraction for pods

Q10: What is the difference between Deployment and StatefulSet?¶

Answer: - Deployment: Stateless apps, random pod names, shared storage - StatefulSet: Stateful apps, ordered pod names, persistent storage per pod

Q11: Explain Kubernetes Services¶

Answer: - ClusterIP: Internal service (default) - NodePort: Exposes service on node's IP - LoadBalancer: External load balancer - ExternalName: Maps to external DNS name

CI/CD¶

Q12: What is CI/CD?¶

Answer: - CI (Continuous Integration): Automatically test code on commit - CD (Continuous Deployment/Delivery): Automatically deploy tested code - Benefits: Faster releases, fewer bugs, automated testing

Q13: Explain GitHub Actions workflow¶

Answer:

name: CI/CD Pipeline
on:
  push:
    branches: [main]
jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - name: Build
        run: docker build -t app .
      - name: Test
        run: npm test
      - name: Deploy
        run: ./deploy.sh

Q14: What is Infrastructure as Code?¶

Answer: - Managing infrastructure through code (Terraform, Ansible, CloudFormation) - Benefits: Version control, reproducibility, consistency - Tools: Terraform, Ansible, Pulumi, CloudFormation

Cloud & AWS¶

Q15: Explain AWS EC2 vs ECS vs EKS¶

Answer: - EC2: Virtual servers, full control - ECS: Container orchestration, AWS-managed - EKS: Kubernetes on AWS, managed control plane

Q16: What is S3 and its use cases?¶

Answer: - Object storage service - Use cases: Static websites, backups, data lakes, content delivery - Features: Versioning, lifecycle policies, encryption

Q17: Explain VPC and subnets¶

Answer: - VPC: Virtual private cloud, isolated network - Subnets: Segments of VPC (public/private) - Route Tables: Control traffic between subnets - Internet Gateway: Connect VPC to internet

System Design¶

Q18: Design a scalable web application¶

Answer: 1. Load balancer (distribute traffic) 2. Web servers (stateless, horizontal scaling) 3. Application servers (business logic) 4. Database (master-slave replication) 5. Caching layer (Redis) 6. CDN (static content) 7. Message queue (async processing)

Q19: How do you ensure high availability?¶

Answer: - Multi-AZ deployment - Load balancing - Auto-scaling - Health checks - Disaster recovery plan - Database replication

Troubleshooting¶

Q20: How do you debug a slow application?¶

Answer: 1. Check application logs 2. Monitor CPU, memory, disk I/O 3. Check database performance 4. Review network latency 5. Use profiling tools 6. Check for memory leaks

Q21: Container keeps restarting, how do you debug?¶

Answer:

# Check logs
docker logs container_name

# Inspect container
docker inspect container_name

# Check exit code
docker ps -a

# Run container interactively
docker run -it image_name /bin/bash

Security¶

Q22: How do you secure containers?¶

Answer: - Run as non-root user - Use minimal base images - Scan images for vulnerabilities - Limit container capabilities - Use secrets management - Network policies

Q23: Explain least privilege principle¶

Answer: - Grant minimum permissions needed - Use IAM roles with specific permissions - Avoid root/admin access - Regular access reviews

Behavioral Questions¶

Q24: Tell me about a time you handled a production incident¶

Answer (STAR Method): - Situation: Production outage affecting users - Task: Restore service quickly - Action: Identified root cause, implemented fix, communicated status - Result: Service restored, post-mortem conducted, prevention measures added

Q25: How do you handle conflicting priorities?¶

Answer: - Assess impact and urgency - Communicate with stakeholders - Document decisions - Focus on business value

Advanced Questions¶

Q26: Explain blue-green deployment¶

Answer: - Two identical environments (blue = current, green = new) - Deploy to green environment - Test green environment - Switch traffic from blue to green - Rollback by switching back to blue

Q27: What is canary deployment?¶

Answer: - Deploy new version to small subset of users - Monitor metrics - Gradually increase traffic - Rollback if issues detected

Q28: Explain microservices vs monolith¶

Answer: - Monolith: Single application, easier to develop, harder to scale - Microservices: Multiple services, independent scaling, more complex - Choose based on team size, complexity, scalability needs

Practice Tips¶

Answer Structure

Direct Answer: Answer the question directly
Explanation: Explain the concept
Example: Provide real-world example
Trade-offs: Mention pros and cons if applicable

Common Mistakes

Don't just list tools, explain why you use them
Don't memorize answers, understand concepts
Ask clarifying questions if needed
Admit when you don't know something

Key Takeaways: - Practice explaining concepts clearly - Understand the "why" behind tools and practices - Use STAR method for behavioral questions - Be honest about what you don't know - Show problem-solving approach

Previous: Troubleshooting

DevOps Interview Questions¶

🎯 Learning Objectives

Linux & System Administration¶

Q1: Explain the difference between kill, killall, and pkill¶

Q2: What is the difference between restart and reload for services?¶

Q3: How do you find files larger than 100MB?¶

Q4: Explain file permissions 755¶

Docker¶

Q5: What is the difference between Docker image and container?¶

Q6: Explain Docker layers¶

Q7: How do you reduce Docker image size?¶

Q8: What is the difference between CMD and ENTRYPOINT?¶

Kubernetes¶

Q9: Explain Kubernetes architecture¶

Q10: What is the difference between Deployment and StatefulSet?¶

Q11: Explain Kubernetes Services¶

CI/CD¶

Q12: What is CI/CD?¶

Q13: Explain GitHub Actions workflow¶

Q14: What is Infrastructure as Code?¶

Cloud & AWS¶

Q15: Explain AWS EC2 vs ECS vs EKS¶

Q16: What is S3 and its use cases?¶

Q17: Explain VPC and subnets¶

System Design¶

Q18: Design a scalable web application¶

Q19: How do you ensure high availability?¶

Troubleshooting¶

Q20: How do you debug a slow application?¶

Q21: Container keeps restarting, how do you debug?¶

Security¶

Q22: How do you secure containers?¶

Q23: Explain least privilege principle¶

Behavioral Questions¶

Q24: Tell me about a time you handled a production incident¶

Q25: How do you handle conflicting priorities?¶

Advanced Questions¶

Q26: Explain blue-green deployment¶

Q27: What is canary deployment?¶

Q28: Explain microservices vs monolith¶

Practice Tips¶

Q1: Explain the difference between `kill`, `killall`, and `pkill`¶

Q2: What is the difference between `restart` and `reload` for services?¶

Q8: What is the difference between `CMD` and `ENTRYPOINT`?¶