In this tutorial, you’ll learn about creating and deploying Docker apps, including using multiple containers with a database, and using Docker Compose. You’ll also deploy your containerized app to Azure.
Start the tutorial
If you’ve already run the command to get started with the tutorial, congratulations! If not, open a command prompt or bash window, and run the command:
docker run -d -p 80:80 docker/getting-started
You’ll notice a few flags being used. Here’s some more info on them:
- -d – run the container in detached mode (in the background)
- -p 80:80 – map port 80 of the host to port 80 in the container
- docker/getting-started – the image to use
You can combine single character flags to shorten the full command. As an example, the command above could be written as:
docker run -dp 80:80 docker/getting-started
The VS Code Extension
Before going too far, we want to highlight the Docker VS Code Extension, which gives you a quick view of the containers running on your machine. It gives you quick access to container logs, lets you get a shell inside the container, and lets you easily manage container lifecycle (stop, remove, and so on).
To access the extension, follow the instructions here. Use the Docker icon on the left to open the Docker view. If you open the extension now, you will see this tutorial running! The container name (angry_taussig below) is a randomly created name. So, you’ll most likely have a different name.
What is a container
Now that you’ve run a container, what is a container? Simply put, a container is simply another process on your machine that has been isolated from all other processes on the host machine. That isolation leverages kernel namespaces and cgroups, features that have been in Linux for a long time. Docker has worked to make these capabilities approachable and easy to use.
Creating Containers from Scratch If you’d like to see how containers are built from scratch, Liz Rice from Aqua Security has a video in which she creates a container from scratch in Go:
What is a container image
When running a container, it uses an isolated filesystem. This custom filesystem is provided by a container image. Since the image contains the container’s filesystem, it must contain everything needed to run an application – all dependencies, configuration, scripts, binaries, and so on. The image also contains other configuration for the container, such as environment variables, a default command to run, and other metadata.
We’ll dive deeper into images later on, covering topics such as layering, best practices, and more.
If you’re familiar with chroot, think of a container as an extended version of chroot. The filesystem is simply coming from the image. But, a container adds additional isolation not available when simply using chroot.
Continue with the tutorial!