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Containers are based on images, and you better should know a bit about images as well.

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So before running a container, the container image is fetched and stored locally.

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All images are stored on the container host by default, and you can use Docker images

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for a list of current images.

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The command docker inspect images is a cool command because it will show you exactly what

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happens while starting the container.

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And if you don't need a specific container image anymore, you can use docker rmi followed

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by the name of the image to remove the image.

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It's also possible to work with custom images.

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To do so, you would use the docker file.

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On Red Hat-based Popman systems, container file is commonly used as an alternative name

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for docker file.

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For an example, you can check the docker file in the course Git repository.

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Now you can build your own container image based on the instructions in the docker file.

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Use docker build minus T image name.

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That's the name of the image that you want to create.

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Dot slash name of the docker file directory to build the container image.

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And after creating the image is added to the list of images on your system.

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Let me show you.

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So to start with, I want to show you docker images.

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These are the images that have been fetched so far.

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And do you see that?

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The busy box is only four megabytes.

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Now let's use docker inspect on NGINX.

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Well I would like to use it in a slightly different way.

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Let's use docker image inspect on NGINX.

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Because docker inspect, you don't tell docker what to expect, so it needs to guess.

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Docker image inspect, it knows that you want to inspect an image.

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Without the image, it will also find the container with the name NGINX and it will show you the

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configuration of that.

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Now here we can see the configuration behind the container image with the path variable,

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with the default commands that it is running, and more about what the container image is

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doing.

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And that can be very useful to figure out what is going to happen before you actually

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do it.

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Now let's go into the course git repository.

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To start with, I need to make it available here using git clone https://github.com

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slash Sander van Vugt slash Linux plus.

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All right, so in the Linux plus git repository, there's a subdirectory with the name dockerfile

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in which you find a dockerfile.

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So what is in this dockerfile?

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Well, a simple example of a dockerfile specifying from Alpine.

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So it's using Alpine, one of these base cloud image as a foundational image.

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Then we have the maintainer.

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That's for politeness sake.

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It's open source and an open source is always nice if you can find your original developer.

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Then we use add to add a file.

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It's kind of a dummy here, but it's an interesting way to show you how you can add a file to

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your container image.

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Then it is installing some cool software.

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The run command is running while you build your custom container image.

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So apk is the Alpine package manager is going to add bash as well as nmap.

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Then the entry point is specifying the default command, and this entry point works with the

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argument minus sn 172.17.0.0.

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So if I want to use it, I can use docker build minus t altmap.

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Minus t is a tag, and this tag is really the name that you are going to assign, and I'm

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doing that on dot.

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Now this is telling you that the legacy builder is defecated.

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Please ignore that.

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For now, it's still used.

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Now if I use docker images, then we can see that altmap is now available.

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And if I use docker run altmap, it is going to run its primary application.

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And its primary application is nmap, and here you can see that nmap is doing its work and

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might give us a result in a little bit.

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It's not about the result of the nmap application.

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It's about the fact that I created a container image that is running this application.

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Why would you want to do that?

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Well, containers are cool because they run in complete isolation.

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No risk for any other applications in your environment.