Dockerfile

A Dockerfile is a simple text file that contains a list of instructions for building a docker image. It defines the environment, software, dependencies, and steps needed to set up and run an application inside a container.

Why Use a Dockerfile?

• Automates the image creation process
• Makes deployments consistent and reproducible
• Easy to share enviroments with others
• Makes it easy to share apps across systems

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Example Dockerfile

This is a simple Dockerfile for a node.js application:

# 1. Use an official Node.js base image
FROM node:18-alpine

# 2. Set the working directory
WORKDIR /app

# 3. Copy package.json and install dependencies
COPY package*.json ./
RUN npm install

# 4. Copy the rest of the application code
COPY . .

# 5. Expose the port the app runs on
EXPOSE 3000

# 6. Define the command to run the app
CMD ["node", "index.js"]

---

Line	Description
FROM node:18-alpine	Uses a lightweight Node.js base image.
WORKDIR /app	Sets /app as the working directory inside the container.
COPY package*.json ./	Copies package files needed for installing dependencies.
RUN npm install	Installs project dependencies.
COPY . .	Copies the rest of your project files.
EXPOSE 3000	Declares that the app runs on port 3000.
CMD ["node", "index.js"]	Tells Docker how to start your app.

.dockerignore

Create a .dockerignore file to exclude unnecessary files from the build context:

node_modules
.git
Dockerfile
docker-compose.yml
...

This speeds up builds and keeps your images clean.

Build & Run Commands

To build and run your Docker image:

docker build -t my-node-app .
docker run -p 3000:3000 my-node-app