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If you are starting your journey into the containerized world, the first thing you'll come across is Docker. This tutorial gives you a quick start by providing you with the tools to play with not Docker, but Podman, Dockerfiles, and the Red Hat Quay container registry. Why Podman you ask? Well podman is a drop in replacement for docker and is Rootless, which makes it much more secure. It's part of the growning Security First mentalitity, so we're going to use Podman under the covers through this tutorial.
Prerequisites
- Docker account. Free pricing plans are available.
- Red Hat Quay.io account. Free trials are available for 30 days.
Estimated time
Completing this tutorial should take you approximately 45 minutes.
Docker
The first thing you need to do is install Podman. There are a few ways to do this, but the first and best place to is by going to the main Podman documentation site. Try to use and maintain the most current version of Podman, and install it for your particular operating system.
The following steps and commands should work on either version, so let's proceed.
Podman CLI
After you have podman installed, bring up a command prompt. During the installation, there is a check that the documentation may ask you to run. We are going to run the following again to make sure everything is working as expected.
To show the power of podman we're just going to alias alias docker=podman (however you do your aliases, ie .bash_aliases or the like) and you'll see you can do everything docker can do and be Rootless!
You should see something similar to the following output. (If you get an error or something that looks nothing like the below, your installation is not set up correctly and you should resolve this before going any farther.)
Congratulations! You have a working docker cough podman cough instance. Let's start playing with it.
The next command I'd like you to try is the following. Depending on your internet access, it could take a little time to run, but luckily it will be cached on your machine, after which we'll revisit in a bit.
As this runs, let's talk about what's happening. When you run the docker command. You're telling Docker that you want the latest copy from the public Docker hub and run it with the shell of /bin/bash.
The command runs off to the Internet, sees the version you have, checks against either the SHA of your cached image, or if you don't have it, pulls it down from Docker Hub.
For clarity's sake, the -it runs it as interactive and creates a tty for the container.
You should see the following now.
Congratulations! You now have your second running Docker container. Go ahead and type exit, and run that docker command again.
Notice how the roots @2de726a5fcb8 and @583c6cec5d41 are different? It's because when you spin up containers this way they are ephemeral. Ephemeral means they only live for the time that they are running, so as soon as you exit it goes away. I'll show you how to do longer lived containers in a little while.
Now let's play around in the container for a second. With a Fedora machine, you have yum so let's install something.
Now you can run vim in your container! Try it out.
If you don't know how to exit vim, type: :q and you should see your command prompt again.
Now type exit again.
And just to reinforce, when your container is gone, any and all changes inside it are gone too.
Dockerfile
Okay, so we can spin up a container and make changes to it, but how do we keep changes around? There are a few ways, and I encourage you to discover them yourself. However, I'll walk you through the most common way, which is by using a Dockerfile.
Back at your command prompt, make a new directory and change the directory by using your $EDITOR of choice to open a new file called Dockerfile.
I'll hit the highlights of Dockerfiles here, but I strongly suggest you take a look at the Best practices for writing Dockerfiles documentation to get a taste of their power.
In your Dockerfile, write out the following:
Save the file and make sure it's called Dockerfile.
Let's talk about what the four previous lines mean.
FROM: creates a layer from thecentos:latestDocker imageRUN: builds your container by installingviminto it and creating a directory called/vimWORKDIR: informs the container where the working directory should be for itENTRYPOINT: is the command that is run when the container starts, instead of/bin/bashlike how we did above
Now let's build this locally. Run the following in the directory that the Dockerfile is located and let's see this come
together:
Note: You should have a different hash eda2652aa25e, so please keep that in mind.
Congratulations! You have built your first Dockerfile and customized Docker container.
Let's give it a run now. Go ahead and run the following command:
You should see vim start up! Remember, :q is how to quit it, and then you should see your command prompt again. You can run this as many times as you'd like and you'll have a new instance of vim each time; but you can't actually save anything or read anything because it's a container right? Let's fix this.
We are going to add a bind mount and volumes to mount the local directory into the container. If you'd like to read more about mounts and volumes, I suggest starting with the Docker documentation about how to use volumes. It's one of the harder concepts, but it's worth your time.
On your command line, create a file called hello, then save the words hello world in it.
Now let's mount the local directory into our container.
Inside of vim, type :e hello. You should see hello world come up! As you can see, you opened the file that you created on the host machine, created a container with vim inside, mounted the directory, and was able to open the file!
If you'd like, you can type i and type something out. Then type :wq when you're done. The container should close out and then you can type the following on your command line:
Note: Obviously, I added this line from my container is what I wrote. You will see whatever you write.
Awesome! Now let's start figuring out how to share this container to the world.
Container registries
I'm going to introduce you to Red Hat offering called Quay.io. It's a cloud-based, open source public container registry that has some neat nice-to-haves built into it. You can host your own if you want to, but this example just uses the public one.
First, go to Quay.io and create an account.
Now, let's log in, and get ourselves situated.
My username is jjasghar. Change the username to be yours. Wonderful, you're now loggged in.
If we want to create a container and push it to Quay, it's actually quite easy. I'll show you the commands and then explain them.
As you can see, I built the container like we did earlier, but I added -t quay.io/jjasghar/vim:latest as the "tag." I tell docker that I'm sending it to a different registry, then to the default Docker Hub, and to my namespace.
After the build is done, I just use docker push quay.io/jjasghar/vim:latest and it's up! (By default, when you push your first container to Quay.io, you must make it public).
Check out the https://quay.io/repository/jjasghar/vim?tab=settings website (substitute jjasghar with your namespace) and click Make public. Now you can pull to any machine that can talk to the Internet!
Next, let's pull your container down by running the following command:
Success! You now know how to create a container and published it to Quay.io.
Summary
Thanks for walking through this with me. Hopefully, you feel more comfortable with some generic docker commands, how Dockerfiles work, and finally how to use a container registry.
So now that you completed this tutorial and know how to use Docker and container registries, what's next? You can further your personal learning with containers and orchestration by going through our Kubernetes learning path. If you're interested in experimenting with Docker some more, try the following tutorials: