01-docker-desktop

Docker Desktop

If you do not yet have Docker Desktop downloaded, go here and download the desktop suited for your hardware.

What is Docker Desktop?

Docker Desktop is an application that includes all programs needed for you to build and share containerized applications on your machine. What is a containerized application you might ask? An application that is containerized can be any application you like that you isolate to run in an environment where you easily can control what versions different dependencies uses and what environment variables it should use. The environment can be on your physical local machine or a remote machine. Usually you start running the containerized application on your physical machine during development and when features are ready to be deployed to production the containerized application will reside on a remote host.

The approach of containerizing an application starts by making a Dockerfile which will be built into an image (More details on Dockerfile in the next chapter) . If then running the image you will get a _ running container_ which you can access by an address and a port. Continue reading for an explanation of how you can interact with Docker Desktop to get information of your local and remote images and containers.

Images

As mentioned, images are the resulting unit you get when telling Docker to build an image based on the content of a Dockerfile. In most cases a Dockerfile includes one or more COPY commands which moves your local files into the Docker image along with some commands that should be executed when the image is used to start a container. Packing this information together inside an image allows for easily sharing and running applications between physical computers.

In Docker Desktop you can manage your images by locating to the images tab. Clicking an image will show how the image was built up based on other images, and how commands in the Dockerfiles from these images result into different layers .

Want to know more about layers?

Layers

In order to understand exactly what a layer is, lets first make it clear that images are based on other images. And all images are based on different commands which will be explained in more detail later in the course. Each time Docker executes a command a new layer is made which is actually the difference between the image before and after the command was executed.

Containers

Also as mentioned, containers are the unit you get when telling Docker to run an image. The commands stated in the Dockerfile has made the foundation of how this container will behave, such as:

• What command will be executed inside the container when you run the image.
• What commands will be executed while making the container.
• What will be the working directory that the commands are executed from.
• What environment variables it uses. to mention some characteristics.

In Docker Desktop you can see the containers that either run or has been stopped on your machine. Clicking into a container will show it's logs, environment variables, resource usage, configuration and even a terminal tab.

Volumes

Since containers are easily terminated because of their light weight, they are not suitable for storing persistent data. When the container dies all the data it has gathered or generated, as well as all state-related data, will be lost forever. That is, however, if you do not have a volume. A volume is simply a directory on the host machine of the running container that the container will use to mount its data up and down to. The only thing the container needs to know is the name of the volume and the path to where in the containers file system it will mount the data to. Docker will then take care of making the actual reference from the containers mount path to the data persisted some where else on the host machine.

In Docker Desktop you can see all volumes on your local machine by locating to the volumes tab on the left-side menu. When clicking on a volume you can see what containers that er using that volume and to what path the container is mounting the data on the volume.

What are bind mounts in comparison?

Bind Mounts

Bind mounts are a simpler way of persisting data on a container, but instead of letting Docker take care of the mounting and referencing, you are explicitly providing the container with a reference path to the host machine.

Resources

Click the cog icon in the top right and then _ Resources_ to manage the CPU and memory allocated to Docker Desktop.]()

🫵🏽 Try yourself

Create a running container by copying the command on the frontpage of Docker Desktop when opening the Containers tab. Open your terminal and enter the command.

docker run -d -p 80:80 docker/getting-started

Task 1.1

Figure out how much memory the container uses.

✅ Answer 1.1

Click on the running container in Docker Desktop and see the Stats tab and see that the container uses 5,4 MB memory.

Task 1.2

Figure out what environment variables that are defined for the container.

✅ Answer 1.2

Click on the running container in Docker Desktop and see the Inspect tab and see that the container has the following 4 environment variables defined:

1. PATH: /usr/local/sbin:/usr/local/bin: /usr/sbin:/usr/bin:/sbin:/bin
2. NGINX_VERSION: 1.23.3
3. PKG_RELEASE: 1
4. NJS_VERSION: 0.7.9

Task 1.3

Figure out how many images the docker/getting-started image is based on.

✅ Answer 1.3

Click on the image named docker/getting-started in Docker Desktop and see that there are 4 FROM instructions in total building up the final image that now resides on your machine.

Task 1.4

Create a volume with this command:

docker volume create workshop-volume

And create a new container that is using that volume:

docker run -d -p 5000:5000 --name workshop-container -v workshop-volume:/data nginx

Figure out where on your local machine the data used by the container is stored, i.e., what is the path to the volume mount?

✅ Answer 1.4

Inspect the container and see the path under Mounts.

/var/lib/docker/volumes/workshop-volume/_data

Task 1.5 - For those who wants an extra challenge 😈

Open the data tab under volumes in Docker Desktop and see that there is no data.

Let's try add some!

Open the terminal of the running container:

docker exec -it workshop-container bash

Locate to the folder where the data from the volume is mounted to and add a file. You see a change in the data tab in Docker Desktop?

💡 Need a tip?

If you wonder where the data is stored in the container take a closer look on the command that started the container:

docker run -d -p 5000:5000 --name workshop-container -v workshop-volume:/data nginx

Especially this part; -v <volume_name>:<path_in_container_to_mount_data> , will tell you where to find the data on the container.

✅ Answer 1.5

After running the docker exec command all you need is the following two lines:

cd data
touch test-file.html

Locating to the data tab under volumes in Docker Desktop after doing this will reveal the newly added file.