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Now in the vast majority of use cases,

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you don't just want to download and run an image

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that gives you an interactive shell

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like the node image does at the moment.

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This is nice to get started

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and to have our first experience with containers and images,

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but it's not all we wanna do.

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Instead, typically you build up on those space images

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to then build your own images.

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Like for example here,

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we could build up on the node image

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to then execute certain node JS code with that image.

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And of course, node is just one example here.

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An example I will use a lot throughout the course,

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but the same would be true for PHP,

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for GO, for Python,

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whichever programming language you're using,

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whichever application you might be building.

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Typically you would pull into your official base image

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and then add your code on top of that

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to execute your code with that image.

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And of course you wanna do all of that

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inside of a container.

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And that is a scenario where you need to build

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your own image because your exact application

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with your code.

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Of course, this does not exist on Docker hub

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unless you shared it dear.

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So therefore, now we'll build our own image

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building up on this node image though,

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and for that I prepared a very simple node JS dummy project

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and you don't need to know node to follow along.

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You can simply download this dummy project.

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You find it attached and it contains four files here,

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a server JS file,

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which contains our main node application code.

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In case you know node,

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you can quickly see what this does

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In case you don't know it,

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this starts a web server with node JS,

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listening on port 80

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and we handle incoming requests to two URLs

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to our domain slash nothing

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if it's a get HTTP request,

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in which case this HTML code will be returned.

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And we handle post requests to store a goal

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where we then try to retrieve a goal key,

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a goal value from the incoming request body.

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We then lock this goal to the console

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and we set some user goal variable equal

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to that extracted goal.

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And then we redirect to the slash route again

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so to this route

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and here we then render HTML code

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where we utilize this user goal variable,

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which has a default value,

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which is eventually overwritten to the entered goal value.

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And this variable is output here.

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This is Java script code executed with node

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to bring up such a node web server.

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But again, you don't need to know node.

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This course is not about node.

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This is just one example application

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which you wanna dockerize,

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which we wanna run in a Docker container.

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Now, two other key things belong to this application.

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One key thing is the public folder,

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which has a CSS file for some styling.

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This file is automatically loaded in the end

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by telling the node server

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to well, just redirect requests to files

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to the public folder

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and then look for such files there,

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which is why I request two styles.

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CSS will load style CSS, which is in the public folder,

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but then probably the more important

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our key thing we have here

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is the package.json file.

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Here, we describe this node application

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and that is a node exclusive concept.

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It has nothing to do with Docker,

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this package.json file.

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But here we tell node

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which dependencies we have,

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which other third party packages

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we need to run this node application

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in this case that's the express framework

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which is a node JS package

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we can use in our node JS applications

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and the body parser package.

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Now, if you would want to run this project locally

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without Docker, you would need to install Node JS

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from nodejs.org.

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For example, that latest version

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and then thereafter in your project folder

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in a terminal opened in that folder.

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And here, this is my default terminal

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just integrated in visual studio code,

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the idea I'm using here,

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automatically navigated into this project folder.

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And in this terminal, you would need to run NPM install.

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NPM is another tool shipping together

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with node JS,

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so being installed automatically

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when you install Node

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and NPM install will now download

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and install all the dependencies we need.

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And then thereafter, once you did this,

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you could execute the server JS file with the node command.

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And this would then start the server

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and on local host, port 80,

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you could visit this application, set your goal

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and see this in action.

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Now this is the node application running locally

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without Docker and you don't need to install Node.

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This was just an example how we would run it without Docker.

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Now, of course, this course is about Docker though.

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So let's quit this with Ctrl + C.

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Let's clear this console

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and let's actually delete the node

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modules folder

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which was created after running NPM install.

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And let's all deletes,

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the package dash lock json file here.

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So that we're back to the initial files.

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The get ignore file, by the way is optional.

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It's just important if you're using

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get for version control.

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So this is now a node application.

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How can we now build our own image

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that contains this application

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and that then also utilizes the node Docker hub image

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to run that code?