Create a container

What is a Container?

A container is a lightweight standalone executable package that contains everything needed to run an application, such as libraries, tools, runtime, settings, or code making it easy to deploy in VMs (Virtual Machines). It can be created as many as possible from a single Docker image

To dockerize a Node.js application, we will need to follow these steps:

• A Node.js Application (which we already have running on port 5000)
• Create a Dockerfile
• Building a Docker Image
• Containerize the Docker image

What is a Dockerfile?

A dockerfile is an ingredient or set of instructions needed to create a docker image(s). It gets to build the image by running the build command.

Create a file in the root directory called Dockerfile.
First, we need to define which image we want to build from.

Here we will use version 16 of the node available as it is the current version of Nodejs as at this time this guide was written from Docker Hub :

FROM node:16.18.0

#Create app directory
WORKDIR /app

#Install the app dependencies using the npm binary.
COPY package*.json  ./
 
RUN npm install

#Copy the rest of the application to the app directory.
COPY . /app
 
#Expose the port and start the application. 
EXPOSE 5000
 
CMD [ "npm", "start" ]

NOTE: Above you will notice we used two distinct COPY commands to reduce the application rebuild time

Create a .dockerignore file

What is a .dockerignore file:
It helps prevent the local module and debug logs from being copied into your Docker image when building a docker image.

Now, let's create a .dockerignorefile file so as not to copy unnecessary files to the container during its built process from the logs.

npm-debug.log
/node_modules

This prevents the local module and debug logs from being interrupted and copied onto your Docker image.

Building your Docker Image

What is a Docker Image:

This is a set of read-only instructions that helps to build a container and makes it possible to run it on a Docker.
Building your Docker image is quite easy and can be done using a single command.

But before building it, look at the image below to confirm you have the displayed files and directories on your code editor. If you can’t or don’t have the codes.

You can fork a folder repo here from this to build yours.

Be sure to have these extensions installed so you can remotely access your docker logs and files via your Vscode just like this image below:

• Docker extension
• Dev Container extension
• Remote SSH extension

On the left section of this picture, you can see the Docker extension, Remote live server, and Dev container extension icons.

Be sure to install and download these two extensions if you are using Vscode (Visual Studio Code) so you can access your images and containers on your visual code editor registry easily.

On the left-hand side of your Vscode via the docker tab.
The docker image on the left pane of the code editor shows that it is installed as an extension and you can also access the Docker hub and Registry within your Vscode environment.

It should look something like this below:

If confirmed, you can run this command on your terminal or CLI tool.

Docker build -t <docker-image-name> <filepath> .

The -t flag lets you tag your image so it’s easier to find later

Here is an example we use in this guide:

Docker build -t nodejs-app .

The result should look like this in the terminal with a message above "FINISHED"

You should get something similar to the output above after executing the command.
This means that the docker image was created successfully and the app is working.

Now that the build is complete, you can check your image or your docker using this docker command below :

docker image ls

Here is the result:

Check Using your Docker Desktop:

• Open your Docker Desktop
• Go to Images on the left side of your docker desktop dashboard

You can see your built Nodejs docker image there.

Create a Container using Docker Desktop:

You will need to create a container from your built image.
You can easily do that using your Docket desktop with the following steps.

1. Go to your Docker desktop and navigate to your Image tab

2. Go to your created and built docker image from your application. The one we used here is named "node-app"

3. Before clicking on "RUN " from the image tab, Click on the “Optional settings “ specify a favorable container name or it will generate a random one for you.
   Then route the host to your local server application

Example: Localhost:5000. By typing your local host port (5000), which is what we are using. Yours can be 8080 or anything.

Launch Run. You have successfully created a container. You can view this via your container tab above the image tab on your Docker desktop.

Navigate to actions and choose "Logs" to view your running container logs.

Navigate to your browser and type in or paste " https://localhost:5000" to view your running container image with display message " Hello world "

Run a Container Using the terminal or command line

Do note that a container can be created as many times as you want.
Now we can run the docker image using the command:

Docker run -d -p <Host port>:<Docker port><docker-image-name>

The -d flag indicates the docker container is running in the background.

The -p flag shows which host port will be connected to the docker port.

Example:

Docker run -d -p 5000:5000 nodejs-app

Result: