Containerization-devops

🐳 Dockerfile, .dockerignore, Tagging & Publishing – Complete Guide

📌 1️⃣ Flask Application with Docker

Project Structure

my-flask-app/
│── app.py
│── requirements.txt
│── Dockerfile
│── Dockerfile.multistage
│── .dockerignore

app.py

from flask import Flask
app = Flask(__name__)

@app.route('/')
def hello():
    return "Hello from Docker!"

@app.route('/health')
def health():
    return "OK"

if __name__ == '__main__':
    app.run(host='0.0.0.0', port=5000)

requirements.txt

Flask==2.3.3

Dockerfile

FROM python:3.9-slim

WORKDIR /app

COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt

COPY app.py .

EXPOSE 5000

CMD ["python", "app.py"]

.dockerignore

__pycache__/
*.pyc
.env
.venv
.vscode/
.idea/
.git/
*.log
tests/

📌 Build & Run Commands

docker build -t my-flask-app .
docker images
docker run -d -p 5000:5000 --name flask-container my-flask-app
docker ps
docker logs flask-container
curl http://localhost:5000

📌 Tagging Images

docker build -t my-flask-app:1.0 .
docker build -t my-flask-app:latest -t my-flask-app:1.0 .
docker tag my-flask-app:latest my-flask-app:v1.0
docker tag my-flask-app:latest username/my-flask-app:1.0

📌 Image Inspection

docker history my-flask-app
docker inspect my-flask-app

📌 Multi-Stage Dockerfile (Optimized)

Dockerfile.multistage

# STAGE 1
FROM python:3.9-slim AS builder

WORKDIR /app
COPY requirements.txt .
RUN python -m venv /opt/venv
ENV PATH="/opt/venv/bin:$PATH"
RUN pip install --no-cache-dir -r requirements.txt

# STAGE 2
FROM python:3.9-slim

WORKDIR /app
COPY --from=builder /opt/venv /opt/venv
ENV PATH="/opt/venv/bin:$PATH"

COPY app.py .

RUN useradd -m -u 1000 appuser
USER appuser

EXPOSE 5000
CMD ["python", "app.py"]

Build Multi-Stage Image

docker build -f Dockerfile.multistage -t flask-multistage .
docker images | grep flask

Expected:

flask-regular ~250MB
flask-multistage ~150MB

📌 Publish to Docker Hub

docker login
docker tag my-flask-app:latest username/my-flask-app:latest
docker push username/my-flask-app:latest
docker pull username/my-flask-app:latest
docker run -d -p 5000:5000 username/my-flask-app:latest

📌 Node.js Application with Docker

Project Structure

my-node-app/
│── app.js
│── package.json
│── Dockerfile

app.js

const express = require('express');
const app = express();
const port = 3000;

app.get('/', (req, res) => {
    res.send('Hello from Node.js Docker!');
});

app.get('/health', (req, res) => {
    res.json({ status: 'healthy' });
});

app.listen(port, () => {
    console.log(`Server running on port ${port}`);
});

package.json

{
  "name": "node-docker-app",
  "version": "1.0.0",
  "main": "app.js",
  "dependencies": {
    "express": "^4.18.2"
  }
}

Node Dockerfile

FROM node:18-alpine

WORKDIR /app

COPY package*.json ./
RUN npm install --only=production

COPY app.js .

EXPOSE 3000

CMD ["node", "app.js"]

Build & Run Node App

docker build -t my-node-app .
docker run -d -p 3000:3000 --name node-container my-node-app
curl http://localhost:3000

📌 Multiple Tag Example

docker build -t myapp:latest -t myapp:v2.0 -t username/myapp:production .

📌 Useful Docker Commands Summary

docker build -t myapp .
docker run -p 3000:3000 myapp
docker ps
docker ps -a
docker images
docker tag myapp:latest myapp:v1
docker push username/myapp
docker pull username/myapp
docker rm container-name
docker rmi image-name
docker exec -it container-name bash
docker container prune
docker image prune
docker system prune -a