How to Call 'npm start' though Docker ?

Docker is a powerful tool for creating, deploying, and running applications inside containers. If you have a Node.js application, you might want to run it inside a Docker container to ensure consistency across different environments. This article will guide you on how to call npm start through Docker to run your Node.js application.

It runs the application in a kind of isolated environment called container. A container is lightweight and contains everything needed to run the application. Multiple containers can run on the same host, and they can also share data between them securely.

Steps to Setup the Application

Step 1: Create a React application using the following command.

npx create-react-app docker-react

Step 2: After creating your project folder(i.e. docker-react), move to it by using the following command.

cd docker-react

Step 3: Create a file named Dockerfile in the root of your app.

Project Structure:

The updated dependencies in package.json file will look like:

"dependencies": {
    "express": "^4.19.2",
  }

Create a Dockerfile

A Dockerfile is a script that contains a series of instructions on how to build a Docker image for your application. Create a Dockerfile in your project directory with the following content:

FROM node:alpine
RUN mkdir /app
WORKDIR /app
COPY package.json /app
RUN npm install
COPY . /app
CMD ["npm", "start"]

Explanation:

• First, we load the base image node:alpine which is a lightweight Linux distribution with a node installed in it.
• Then we copy the package.json file which contains the app's dependencies into our working directly.
• And then we install the dependencies and copy the project files into our working directory.
• Finally, we run the command npm start.

Creating docker image:

Run the following command from the project's root directory. Make sure your docker daemon is running.

docker build -t <yourname/projectname> .

Steps to run the application:

Run the application using following command from the root directory of your folder.

docker run -d -it -p 3000:3000 <yourname/projectname>

Here we need to map our localhost port to the one of the container which in our case is 3000.

Output: Now open your browser and go to http://localhost:3000/, you will see the following output.

Conclusion

Running npm start through Docker allows you to encapsulate your Node.js application in a container, ensuring that it runs consistently across different environments. By following the steps in this article, you can build and run a Docker container for your Node.js application, leveraging the power of Docker for development, testing, and deployment. This approach enhances the portability and scalability of your application.