How to Deploy a Node.js Application with Docker?

Requirements

This script assumes that you have a Node.js application with a package.json file and a start script specified in it. If you don't have an existing Node.js application, you can create a simple one by running npm init and npm install express.

Create a Dockerfile

First we will write a Dockerfile. We will use an official Node.js runtime as the base image

FROM node:14

Next we set the working directory in the container

WORKDIR /app

Now we copy the package.json and package-lock.json to the container

COPY package*.json ./

The package.json file is the heart of any Node project. It records important metadata about a project which is required before publishing to NPM, and also defines functional attributes of a project that npm uses to install dependencies, run scripts, and identify the entry point to our package. Source
The package-lock.json is automatically generated for any operations where npm modifies either the node_modules tree, or package. json . It describes the exact tree that was generated, such that subsequent installs are able to generate identical trees, regardless of intermediate dependency updates. Source

Next we install the dependencies in our case npm install will search for all and do this for us

RUN npm install

So know we copy the rest of the applicaiton code from our current directory (.) to the current directory in the container

COPY . .

Last but not least, we need to specify the command to run when the contianer starts. So we want to run npm start to start our application

CMD [ "npm", "start" ]

Build the Docker image

docker build -t my-node-app:v1.0.0 .

-t (or --tag) is the only required paramter together with the location of the files for the image and is used to give the image a name and if you want (recommended) a version.
Example -t imagename:v1.0.0

Run the Docker container

We wrote a Dockerfile and built the Docker image, so now it's time to run our container. To do this we need to execute only one command.

docker run -p 3000:3000 my-node-app:v1.0.0

With the -p or --publish parameter we define a Port to publish our application outside of the container, since our container runs in isolation, which includes the networking part. So the format is: host port:container port (host port = port to access from outside, container port = the port in the container). As we can see, we have access in the webbrowser with http://localhost:3000 or in general IP-Address:Port.

How to publish a Docker image to Docker Hub?

To publish your Docker image tho a Docker registry (e.g. Docker Hub). Make sure you have a Docker Hub Account and then type in following three commands:

docker login
docker tag my-node-app /my-node-app:v1.0.0
docker push /my-node-app

And that's it! Your Node.js application is now deployed and running inside a Docker container.