Creating the Dockerfile

Inside our test application, create a new file called Dockerfile (capital D, no extension):

FROM node

ENV MONGO_DB_USERNAME=admin \
    MONGO_DB_PASSWORD=qwerty

RUN mkdir -p /home/app

COPY . /home/app

CMD ["node", "/home/app/server.js"]

Important Note About CMD Path

Since we are inside the test-app folder during development and can run:

node server.js

directly, everything works locally.

But when the Docker container runs, we will be at the root filesystem level, where no server.js exists in the same location.

That is why we write the complete path:

/home/app/server.js

So Docker knows exactly where the file is inside the container.

Building a Docker Image From the Dockerfile

To build a Docker image from the Dockerfile, run:

docker build -t test-app:1.0 .

Explanation

• -t → tag (image name + version)
• test-app:1.0 → image name and version
• . → current directory (where Dockerfile exists)

Important Note

Run this command inside the test-app folder because that is where the Dockerfile is located.

After Build Completion

Verify the image:

docker images

Now you will see:

• test-app:1.0
• mongo
• mongo-express

Running the Container

docker run test-app:1.0

Output

You will see:

Server running on port 5050

This means:

• A container was created
• The Node.js application is running inside the container
• The app is successfully Dockerized

Running in Interactive Mode

docker run -it test-app:1.0 /bin/bash

Inside the Container

Once inside, if we run:

ls

We will see that:

• The test-app folder and all files have been successfully copied into the container
• The application code is available inside the Docker environment

Summary

• Dockerfile defines how the image is built
• docker build creates an image from the Dockerfile
• docker run starts a container from the image
• Application code is copied into /home/app inside the container
• Node.js app runs using CMD
• Everything runs in an isolated Docker environment