The image you provided outlines a general workflow for using Docker to develop, test, and deploy an application. Here's an explanation of each step with an example:

1. Develop
   • Write your application code: This is the initial step where you write the code for your application. For example, let's say you're building a simple Node.js web application.

   // app.js
   const express = require('express');
   const app = express();

   app.get('/', (req, res) => {
     res.send('Hello, Docker!');
   });

   app.listen(3000, () => {
     console.log('Server is running on port 3000');
   });

1. Dockerfile
   • Create a Dockerfile that defines the environment and dependencies for your application: A Dockerfile is a text document that contains the commands to assemble an image. Here’s an example Dockerfile for the above Node.js application.

   # Use an official Node.js runtime as a parent image
   FROM node:14

   # Set the working directory in the container
   WORKDIR /usr/src/app

   # Copy the package.json and package-lock.json files
   COPY package*.json ./

   # Install the dependencies
   RUN npm install

   # Copy the rest of the application code
   COPY . .

   # Expose the port the app runs on
   EXPOSE 3000

   # Command to run the application
   CMD ["node", "app.js"]

1. Build Image
   • Use docker build to create a Docker image from your Dockerfile: This command creates an image from your Dockerfile.

   docker build -t my-node-app .

This command builds an image named my-node-app.

1. Run Container
   • Use docker run to launch a container from your image: This command creates a container from your image and runs it.

   docker run -p 3000:3000 my-node-app

This command runs the container and maps port 3000 of the container to port 3000 of the host machine. Now, if you navigate to http://localhost:3000 in your browser, you should see "Hello, Docker!"

1. Test
   • Test your application within the container: Ensure your application works as expected within the container. If you make changes to your code, rebuild the image and recreate the container.

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

1. Push (Optional)
   • Use docker push to share your image on a registry (e.g., Docker Hub): If you want others to use your Docker image, you can push it to a registry like Docker Hub.

   docker tag my-node-app mydockerhubusername/my-node-app
   docker push mydockerhubusername/my-node-app

1. Pull (Optional)
   • Others can use docker pull to download your image and run your application in their own environments: If someone else wants to use your application, they can pull your image from the Docker registry and run it on their own machine.

   docker pull mydockerhubusername/my-node-app
   docker run -p 3000:3000 mydockerhubusername/my-node-app

This process ensures that your application is containerized, making it easy to deploy and run consistently across different environments.