Example of image creation

Java

Directory structure:

.
├── Dockerfile
├── target
│   └── my-app.jar        # Compiled JAR — only this and the Dockerfile are needed to build the image
├── src
│   └── ...
└── pom.xml

Dockerfile:

# Use an Alpine-based OpenJDK 8 image — Alpine keeps the image size small
FROM openjdk:8-jdk-alpine

# Copy the compiled JAR into the image root
COPY ./target/my-app.jar /

# Start the application when the container launches
ENTRYPOINT ["java", "-jar", "/my-app.jar"]

Tip: For production Java applications, consider multi-stage builds to keep the final image lean: compile in a JDK stage, then copy only the JAR into a JRE-only runtime stage.

PHP

Directory structure:

.
├── Dockerfile
├── entrypoint.sh          # Startup script that launches PHP-FPM and Nginx
├── php
│   ├── index.php
│   └── phpinfo.php
├── nginx
│   ├── nginx.conf
│   ├── conf.d
│   │   └── default.conf
│   ├── fastcgi_params
│   └── ...

Dockerfile:

# Use an Alpine-based PHP-FPM image — PHP-FPM handles PHP processing, Nginx handles HTTP
FROM php:8.2-fpm-alpine

# Install Nginx into the same container to serve as the HTTP frontend
RUN apk add --no-cache nginx

# Copy Nginx configuration files
COPY nginx/ /etc/nginx/

# Copy PHP application files to the web root
COPY php/ /var/www/html/

# Copy and enable the startup script
COPY entrypoint.sh /entrypoint.sh
RUN chmod +x /entrypoint.sh
ENTRYPOINT ["/entrypoint.sh"]

Startup script (entrypoint.sh):

#!/bin/sh

# Start PHP-FPM in the background so Nginx can forward PHP requests to it
php-fpm -D

# Verify PHP-FPM started successfully before launching Nginx
if ! pgrep "php-fpm" >/dev/null
then
    echo "PHP-FPM failed to start!"
    exit 1
fi

# Run Nginx in the foreground — the container stays alive as long as Nginx runs
nginx -g "daemon off;"

Python

Directory structure:

.
├── Dockerfile
├── entrypoint.sh
├── my_app
│   ├── requirements.txt
│   ├── main.py
│   └── my_package
│       ├── __init__.py
│       └── ...

Dockerfile:

# Use the official Python 3.9 image
FROM python:3.9

# Copy the application code into the image
RUN mkdir -p /my_app
COPY my_app/ /my_app/

# Install Python dependencies declared in requirements.txt
RUN pip install -r /my_app/requirements.txt

# Copy and enable the startup script
COPY entrypoint.sh /entrypoint.sh
RUN chmod +x /entrypoint.sh
ENTRYPOINT ["/entrypoint.sh"]

Startup script (entrypoint.sh):

#!/bin/sh

# Start the Flask app using Gunicorn with 3 worker processes, listening on port 8080
# Flask and Gunicorn are declared as dependencies in requirements.txt
gunicorn -w 3 -b 0.0.0.0:8080 my_app.main:app

Node.js

This example covers a frontend project whose static assets are served by Nginx.

Directory structure:

.
├── Dockerfile
├── nginx-conf
│   ├── nginx.conf
│   ├── conf.d
│   │   └── default.conf
│   └── ...
├── package.json
├── src
│   └── ...
└── dist                   # Static files generated by your build step (e.g., npm run build)
    ├── index.html
    └── static
        └── ...

Dockerfile:

# Use Nginx 1.22 as the base image — it provides the startup command, so no ENTRYPOINT is needed
FROM nginx:1.22

# Copy the built static files to Nginx's default serving directory
COPY ./dist /usr/share/nginx/html/

# Copy your Nginx configuration files
COPY ./nginx-conf /etc/nginx/

Run your build step (for example, npm run build) before running docker build. The dist directory must exist in your project root.