🚀 Day 29 – Mock Interview: 50 Questions + Detailed Answers
Series: 30 Days DevOps Interview Preparation
Author: Tathagat Gaikwad
Welcome to Day 29 of the 30 Days of DevOps Interview Preparation Challenge! 🎯
Today, we are simulating a mock interview with 50 real questions that a 1–3 YOE (Years of Experience) DevOps/SRE/Cloud Engineer might face. Each question is paired with a theoretical explanation and a detailed answer to help you build strong confidence.
🔹 Linux & Basics
1. What is the difference between a process and a thread?
A process is an independent unit of execution with its own memory space.
A thread is a lightweight execution unit within a process that shares memory and resources.
✅ Threads are faster, but processes are more isolated.
2. How do you check which process is consuming high CPU in Linux?
Use top, htop, or ps -eo pid,ppid,cmd,%mem,%cpu --sort=-%cpu.
✅ This lists processes sorted by CPU usage.
3. What is the difference between hard link and soft link?
Hard link: Points directly to the inode; original and link are indistinguishable.
Soft link (symlink): A pointer to the file name. If the target is deleted, the symlink breaks.
✅ Example:ln file1 file2(hard link),ln -s file1 file2(soft link).
4. How does the ping command work internally?
It uses ICMP protocol (layer 3, network layer) to send Echo Request and waits for Echo Reply.
✅ Helps test reachability and round-trip time.
5. What are inodes in Linux?
Inodes store metadata (file size, permissions, timestamps, block location) but not the filename.
✅ File names are stored in the directory entry.
🔹 Git & Version Control
6. How do you revert a commit in Git?
Use git revert <commit_id> → Creates a new commit that undoes the changes.
✅ Different from git reset which rewrites history.
7. What is the difference between git fetch and git pull?
git fetch: Downloads changes but doesn’t merge.git pull: Fetches + merges into current branch.
8. How do you resolve merge conflicts in Git?
Edit conflict markers in the file, choose changes, then:
git add <file>
git commit
9. Explain Git branching strategy (GitFlow vs Trunk Based).
GitFlow: Separate branches for feature, release, hotfix. Good for complex projects.
Trunk Based: Small commits merged into
mainquickly. Good for CI/CD.
10. What’s the difference between git merge and git rebase?
Merge: Creates a new commit combining histories.
Rebase: Moves commits to the tip of another branch for a cleaner history.
🔹 CI/CD
11. What is Continuous Integration and Continuous Delivery?
CI: Developers frequently merge code into main branch; automated builds/tests validate it.
CD: Ensures tested code is automatically deployable to staging/production.
12. Difference between Jenkins and GitHub Actions?
Jenkins: Open-source, plugin-rich, requires hosting.
GitHub Actions: Cloud-native, tightly integrated with GitHub repos.
13. How do you secure secrets in CI/CD pipelines?
Use secret managers (Vault, AWS Secrets Manager, GitHub Secrets).
Never hardcode credentials.
Rotate and audit keys.
14. How to trigger a pipeline only on main branch?
Example in GitHub Actions:
on:
push:
branches:
- main
15. Explain the concept of Blue-Green Deployment.
Two environments (Blue\=current, Green\=new). Traffic switches to Green after validation.
✅ Reduces downtime and rollback is easier.
🔹 Docker & Containers
16. What is the difference between Docker image and Docker container?
Image = blueprint (read-only).
Container = running instance of an image.
17. What happens when you run docker run -d nginx?
Docker pulls image (if not present), creates a container, runs it in detached mode.
18. How do you reduce Docker image size?
Use smaller base images (e.g.,
alpine).Multi-stage builds.
Clean package caches.
19. What is a Docker volume?
Persistent storage that lives outside containers.
✅ Example: docker run -v mydata:/data alpine
20. Difference between Docker Compose and Kubernetes?
Docker Compose: Local multi-container orchestration.
Kubernetes: Production-grade container orchestration.
🔹 Kubernetes
21. Difference between Deployment, StatefulSet, and DaemonSet?
Deployment: Stateless apps.
StatefulSet: Stateful apps (databases).
DaemonSet: Runs one pod per node (monitoring/logging agents).
22. What is a Kubernetes namespace?
A logical partition to isolate resources.
✅ Helps multi-team clusters.
23. How do you scale pods in Kubernetes?
kubectl scale deployment nginx --replicas=5
Or use HPA (Horizontal Pod Autoscaler).
24. Explain readiness probe vs liveness probe.
Readiness probe: Checks if pod is ready to serve traffic.
Liveness probe: Checks if pod is still alive or needs restart.
25. What is the difference between NodePort, ClusterIP, and LoadBalancer service?
ClusterIP: Internal access only.
NodePort: Exposes service on every node’s IP:Port.
LoadBalancer: Provisioned cloud load balancer.
🔹 Terraform & IaC
26. What is Infrastructure as Code (IaC)?
Managing infra using machine-readable config files instead of manual setup.
27. What’s the difference between terraform apply and terraform plan?
plan: Shows what will change.apply: Executes the changes.
28. How do you manage Terraform state in teams?
Use remote backends (S3 + DynamoDB, Terraform Cloud).
Lock state to prevent conflicts.
29. What is a Terraform module?
A reusable set of Terraform configs grouped together.
30. Explain terraform import.
It imports existing infra into Terraform state.
🔹 Cloud (AWS/Azure/GCP)
31. Difference between Load Balancer and API Gateway?
Load Balancer: Distributes traffic to servers.
API Gateway: Manages API requests, rate-limiting, auth.
32. What is Auto Scaling?
Automatically adjusts compute capacity based on demand.
33. What is the difference between S3 and EBS?
S3: Object storage, infinite scalability.
EBS: Block storage, tied to EC2.
34. How do you secure credentials in AWS?
Use IAM roles instead of keys.
Store in AWS Secrets Manager/SSM.
Rotate regularly.
35. What are IAM roles and policies?
Roles: Temporary credentials for AWS resources.
Policies: JSON docs defining permissions.
🔹 Monitoring & Logging
36. Difference between Prometheus and Grafana?
Prometheus: Metrics collection + alerting.
Grafana: Visualization/dashboarding.
37. How do you set up alerts for high CPU utilization?
Define Prometheus alert rule.
Send to Alertmanager → Slack/Email.
38. What is log aggregation?
Centralizing logs (e.g., ELK/EFK stack) for analysis.
39. Explain distributed tracing.
Tracking a request across multiple services (Jaeger, Zipkin).
✅ Helps troubleshoot microservices.
40. How would you troubleshoot high latency in an application?
Check app logs.
Monitor CPU/memory/network.
Use APM tools (Datadog, New Relic).
🔹 Networking & Security
41. What is the difference between TCP and UDP?
TCP: Reliable, connection-oriented.
UDP: Faster, connectionless, no guarantee.
42. Explain the concept of a reverse proxy.
A server that forwards client requests to backend servers (e.g., Nginx).
43. What is DNS and how does it work?
DNS translates domain names → IP addresses.
Steps: Resolver → Root → TLD → Authoritative server.
44. What is the difference between a VPN and a VPC?
VPN: Secure private connection over the internet.
VPC: Isolated virtual network inside cloud.
45. How do you secure communication between microservices?
Use mTLS (mutual TLS).
Service mesh (Istio, Linkerd).
API Gateway with auth.
🔹 Behavioral & Scenario-based
46. Tell me about a time you fixed a major production issue.
✅ Use STAR (Situation, Task, Action, Result). Example: Fixed downtime by scaling pods + optimizing DB query.
47. How do you prioritize multiple incidents happening at once?
Severity-based triage.
Critical issues first.
Communicate with stakeholders.
48. How do you handle conflict between development and operations teams?
Promote blameless culture.
Use monitoring + automation to reduce manual errors.
Encourage DevOps mindset.
49. If a deployment fails, what are your next steps?
Check pipeline logs.
Rollback to stable version.
Run root cause analysis (RCA).
50. How do you keep yourself updated with new DevOps tools and practices?
Blogs, newsletters (DevOps.com, CNCF).
Hands-on labs (Katacoda, KodeKloud).
Community groups & meetups.
✨ Final Tips
Practice answers with real-world project examples.
Don’t memorize, understand concepts.
Communicate clearly in interviews.
Review this list multiple times before interviews.
💡 Tomorrow (Day 30), we’ll wrap up this challenge with a final revision strategy + resources 🎯
