🚀 Day 14 of 30 Days DevOps Interview Preparation

Tathagat GaikwadTathagat Gaikwad
7 min read

Series: 30 Days DevOps Interview Preparation
Author: Tathagat Gaikwad

📌 Week 2 Revision + 20 CI/CD Interview Questions (with AWS Practical)

In my 30 Days DevOps Interview Preparation journey, I’ve reached Day 14, which is dedicated to:
✅ Revising all Week 2 concepts (Git, CI/CD, Jenkins, GitHub Actions, Docker)
✅ Answering 20 common CI/CD interview questions
✅ Doing a small AWS practical to apply CI/CD in real-world cloud environments

🔄 Week 2 Quick Revision

1️⃣ Git & GitHub

  • Version control to manage source code.

  • Branching strategies (GitFlow, trunk-based).

  • Importance of pull requests and code reviews in CI/CD.

2️⃣ Jenkins & GitHub Actions

  • Jenkins = self-hosted automation server with plugins.

  • GitHub Actions = cloud-native CI/CD tightly integrated with GitHub.

  • Both enable Pipeline as Code.

3️⃣ Docker Basics

  • Containerization for consistent runtime environments.

  • Used in CI/CD pipelines for build → test → deploy.

4️⃣ CI/CD Recap

  • CI = frequently integrating code & running automated tests.

  • CD = automating deployments to staging/production.

  • Goal → reduce deployment time, minimize errors, and ensure consistency.

☁️ Practical: Deploy a Docker App via CI/CD on AWS

Let’s build a simple CI/CD pipeline on AWS using GitHub Actions.

🔹 Step 1: Setup AWS Infrastructure

  • Create EC2 instance (Ubuntu) for hosting app.

  • Install Docker:

      sudo apt update -y
  sudo apt install docker.io -y
  sudo systemctl enable docker
  sudo systemctl start docker

  • Allow inbound port (80) in EC2 Security Group.

🔹 Step 2: Dockerize Your App

Dockerfile for Node.js app:

FROM node:16
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
EXPOSE 3000
CMD ["npm", "start"]

🔹 Step 3: Push Code to GitHub

Repo structure:

.
├── app.js
├── Dockerfile
├── package.json
└── .github/
    └── workflows/
        └── ci-cd.yml

🔹 Step 4: GitHub Actions CI/CD Pipeline

.github/workflows/ci-cd.yml:

name: CI/CD on AWS EC2

on:
  push:
    branches: [ "main" ]

jobs:
  deploy:
    runs-on: ubuntu-latest

    steps:
      - name: Checkout code
        uses: actions/checkout@v3

      - name: Build Docker image
        run: docker build -t myapp:latest .

      - name: Save Docker image
        run: docker save myapp:latest | gzip > myapp.tar.gz

      - name: Copy image to EC2
        uses: appleboy/scp-action@v0.1.7
        with:
          host: ${{ secrets.AWS_HOST }}
          username: ubuntu
          key: ${{ secrets.AWS_SSH_KEY }}
          source: "myapp.tar.gz"
          target: "~/"

      - name: Deploy on EC2
        uses: appleboy/ssh-action@master
        with:
          host: ${{ secrets.AWS_HOST }}
          username: ubuntu
          key: ${{ secrets.AWS_SSH_KEY }}
          script: |
            docker load < myapp.tar.gz
            docker stop myapp || true
            docker rm myapp || true
            docker run -d -p 80:3000 --name myapp myapp:latest

🔹 Step 5: Test Deployment

  • Access app via EC2 public IP → http://<ec2-public-ip>

  • Each push to main branch triggers build & deploy 🚀

🎯 20 CI/CD Interview Questions & Detailed Answers

1. What is CI/CD in DevOps?

Answer: CI (Continuous Integration) automates code build and test when developers push changes. CD (Continuous Delivery/Deployment) automates app release to staging or production. It reduces human errors, speeds up release cycles, and ensures consistent deployments.

2. Difference between Continuous Delivery vs Deployment?

Answer:

  • Continuous Delivery: Code is always ready to deploy but requires manual approval for production.

  • Continuous Deployment: Every successful pipeline automatically goes to production with no manual steps.

3. Why is CI/CD important?

Answer: It shortens development cycles, improves collaboration, reduces deployment risks, and improves customer experience with frequent updates.

Answer: Jenkins, GitHub Actions, GitLab CI, Bitbucket Pipelines, CircleCI, ArgoCD.

5. How do you secure a CI/CD pipeline?

Answer: Use secret managers (AWS Secrets Manager, HashiCorp Vault), role-based access, signed artifacts, and vulnerability scanning (Trivy, Snyk).

6. What is pipeline as code?

Answer: Writing pipelines in code (e.g., Jenkinsfile, .github/workflows/ci.yml). Ensures version control and reusability.

7. What is Blue-Green Deployment?

Answer: Maintain two environments (Blue = live, Green = idle). Deploy new version to Green, then switch traffic. Ensures zero downtime.

8. What is Canary Deployment?

Answer: Gradually release a new version to a small % of users, monitor, and then expand. Reduces risk of failures.

9. How do you rollback in CI/CD?

Answer: Redeploy previous stable artifact, or use infrastructure automation to restore last state (Terraform, Helm rollback).

10. What is an artifact repository?

Answer: Storage for build outputs like JARs, Docker images (Nexus, Artifactory, AWS ECR, GitHub Packages).

11. What are the common stages in a CI/CD pipeline?

Answer:

  • Source → Code commit triggers pipeline.

  • Build → Compile, package, containerize app.

  • Test → Unit, integration, security, performance tests.

  • Deploy → Deploy to staging/production.

  • Monitor → Logs, alerts, and feedback loop.

12. What are the challenges in setting up CI/CD?

Answer:

  • Handling environment differences (dev vs prod).

  • Securing secrets and credentials.

  • Managing large monolithic apps.

  • Flaky tests causing false pipeline failures.

  • Cost optimization in cloud CI/CD.

13. How do you integrate testing in CI/CD?

Answer:

  • Use unit tests during build stage.

  • Integration tests on staging environment.

  • Security scans (SAST/DAST) integrated into pipeline.

  • Tools: JUnit, PyTest, Selenium, OWASP ZAP, SonarQube.

14. What is Infrastructure as Code (IaC) in CI/CD?

Answer:
IaC automates infrastructure provisioning alongside application deployment. Example: Terraform creates an AWS EC2 + S3 bucket as part of pipeline → ensuring consistency across environments.

15. How does monitoring fit into CI/CD?

Answer:
Monitoring tools (Prometheus, Grafana, CloudWatch) detect performance issues post-deployment. Integrated feedback loops help developers roll back or fix quickly, closing the DevOps lifecycle.

16. What’s the difference between Jenkins and GitHub Actions?

Answer:

  • Jenkins: Open-source, self-hosted, plugin-rich, more customizable but requires maintenance.

  • GitHub Actions: Cloud-native, easy integration with GitHub repos, YAML pipelines, but limited flexibility outside GitHub ecosystem.

17. How do you handle secrets in pipelines?

Answer:

  • Store in AWS Secrets Manager, HashiCorp Vault, or Kubernetes Secrets.

  • Never hardcode credentials in pipelines.

  • Use encrypted GitHub Secrets or Jenkins credentials plugin.

18. How do you achieve zero downtime deployment?

Answer:

  • Use Blue-Green deployments.

  • Use Rolling updates in Kubernetes.

  • Load balancers to gradually shift traffic without downtime.

19. What’s the difference between CI/CD in monoliths vs microservices?

Answer:

  • Monolith: One pipeline builds & deploys the whole app.

  • Microservices: Each service has its own pipeline → independent builds, testing, and deployments.

20. How do you measure CI/CD success?

Answer:

  • Deployment Frequency (how often code is released).

  • Lead Time for Changes (commit → production time).

  • Mean Time to Recover (MTTR) (rollback/recovery speed).

  • Change Failure Rate (deployment issues %).
    These are the DORA metrics widely used in DevOps.

📖 Theory Expansion: CI/CD in Real-World AWS Use Cases

🔹 AWS Native CI/CD Services

  • CodeCommit → Source repo (like GitHub).

  • CodeBuild → Build & test automation.

  • CodeDeploy → Automated deployments (EC2, ECS, Lambda).

  • CodePipeline → Orchestrates the flow (source → build → deploy).

👉 AWS offers a fully managed CI/CD ecosystem, reducing overhead for smaller teams.

🔹 CI/CD Security Best Practices

  • Principle of Least Privilege (PoLP) in IAM roles.

  • Enable artifact signing for integrity.

  • Add static code analysis (SonarQube, Checkov).

  • Integrate container scanning with Trivy or AWS ECR scan.

🔹 Common Real-Life Scenario Asked in Interviews

Q: How would you deploy a Dockerized microservice on AWS with CI/CD?
Answer:

  1. Developer pushes code → GitHub triggers pipeline.

  2. GitHub Actions builds Docker image → pushes to AWS ECR.

  3. AWS CodeDeploy or ECS updates container → runs new task.

  4. Monitoring via CloudWatch + Prometheus for rollback triggers.

🔑 Key Takeaways (Day 14)

✔️ Revised Week 2 concepts: Git, CI/CD, Docker, Jenkins, GitHub Actions.
✔️ Deployed a Docker app via GitHub Actions → AWS EC2 (hands-on).
✔️ Answered 20 CI/CD Interview Questions with detailed theory + real-life AWS examples.
✔️ Learned CI/CD metrics (DORA) → key in SRE/DevOps interviews.

💬 Question for you: Do you prefer AWS-native CI/CD (CodePipeline) or third-party (Jenkins/GitHub Actions)? Why?

#DevOps #AWS #CICD #Docker #Jenkins #GitHubActions #SRE #CloudEngineer #InterviewPreparation #30DaysOfDevOps

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Tathagat Gaikwad
Tathagat Gaikwad