🚀 Day 17 of DevOps Interview Preparation – Push Image to DockerHub

Series: 30 Days DevOps Interview Preparation
Author: Tathagat Gaikwad

Welcome to Day 17 of the 30 Days DevOps Interview Preparation Challenge!
Today we dive into a core DevOps workflow – pushing Docker images to DockerHub, which is the bridge between local development and collaborative deployments in CI/CD pipelines.

---

🔹 What is DockerHub?

DockerHub is a cloud-based container image registry where developers and DevOps engineers can:

• Store, manage, and distribute Docker images.

• Use public repositories for open-source projects.

• Use private repositories for enterprise use cases.

• Automate builds and scanning for vulnerabilities.

In short: Build locally → Push to DockerHub → Pull anywhere.

---

🛠️ Practical: Push Docker Image to DockerHub (on AWS EC2)

Let’s walk through the step-by-step guide.

Step 1: Setup Environment

Launch an AWS EC2 instance (Amazon Linux 2 or Ubuntu).

# Update system
sudo apt-get update -y

# Install Docker
sudo apt-get install docker.io -y

# Start Docker service
sudo systemctl start docker
sudo systemctl enable docker

# Add user to docker group (avoid sudo)
sudo usermod -aG docker $USER

Re-login to apply changes.

---

Step 2: Create DockerHub Account

1. Go to hub.docker.com

2. Sign up and create a repository (e.g., tathagatgaikwad22/myapp).

---

Step 3: Build a Docker Image

Create a simple Node.js app:

app.js

const express = require("express");
const app = express();
app.get("/", (req, res) => res.send("Hello from DockerHub!"));
app.listen(3000, () => console.log("App running on port 3000"));

Dockerfile

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

Build the image:

docker build -t myapp:latest .

---

Step 4: Tag the Image

DockerHub requires tagging with your username/repo:tag format:

docker tag myapp:latest tathagatgaikwad22/myapp:v1

---

Step 5: Login and Push to DockerHub

docker login
# enter DockerHub username & password

docker push tathagatgaikwad22/myapp:v1

---

Step 6: Verify the Image

Go to DockerHub → Repositories, and you’ll see myapp:v1.
Now anyone can pull it with:

docker pull tathagatgaikwad22/myapp:v1
docker run -d -p 3000:3000 tathagatgaikwad22/myapp:v1

---

📖 Theory: Why Push to DockerHub?

• Centralized Registry – Images are available globally.

• Version Control – Tagging allows multiple versions (dev, prod, v1, v2).

• Collaboration – Teams can pull consistent images.

• Integration – Works seamlessly with Kubernetes, AWS ECS, Jenkins, GitHub Actions.

• Security – Private repos and vulnerability scanning.

---

🎯 Interview Questions & Answers

🔹 Q1. Why do we use DockerHub instead of just local images?

👉 Because local images are limited to a machine. DockerHub makes them globally accessible, versioned, and sharable across teams & CI/CD pipelines.

🔹 Q2. Difference between docker push and docker save?

👉 docker push uploads an image to a remote registry (e.g., DockerHub).
👉 docker save exports an image to a local tar file.

🔹 Q3. How do you secure Docker images in DockerHub?

👉 Use private repositories, enable image scanning, follow least privilege access policies, and avoid storing secrets in images.

🔹 Q4. What’s the difference between DockerHub and AWS ECR?

👉 DockerHub → Public, general-purpose container registry.
👉 AWS ECR → AWS-managed private registry, integrated with ECS, EKS, IAM for enterprise use cases.

🔹 Q5. How do CI/CD pipelines use DockerHub?

👉 After CI builds & tests an app → image is tagged & pushed to DockerHub → CD systems (like Kubernetes or ECS) pull images for deployment.

---

✅ Key Takeaways

• DockerHub is GitHub for containers.

• Always tag images meaningfully (latest, v1.0, dev).

• Security is critical: scan and restrict access.

• Pushing to DockerHub is a DevOps fundamental that connects dev → CI/CD → production.

---

💬 Question for you:
👉 Do you prefer DockerHub or cloud-native registries (ECR, ACR, GHCR) for production use?

#DevOps #Docker #DockerHub #CICD #InterviewPreparation #AWS