Where can I learn Docker fundamentals?

ryapric, 10 months ago

Echoing the sentiment that you should adjust your perspective in approaching containerization, otherwise you’re in for a tough time.

Jerome Petazzoni, one of the more recognizable names in the container community, has a site where he puts all of his workshops, slides, etc. This is his one for getting started with Docker.

spez_, 10 months ago

Is there a PDF

ryapric, 10 months ago

Not that I’m aware of, but the source Markdown files are here, so you could probably make one with e.g. pandoc if you wanted.

dartanjinn, 10 months ago

Huge thanks for this. I’ll look at them tonight.

ColdCreasent, 10 months ago

Lots of great information and suggestions in this discussion. Thank you everyone who are offering your input. I’d like to ask as well, how easy is it to setup docker for use in windows? I ask this because almost every guide I’ve found has docker running in Linux. I realize you are able to setup a docker in windows, but I was struggling to get basic instructions for windows, and even the tutorial in docker required me to switch back to docker types that don’t work in windows.

nekusoul, 10 months ago

From my experience the “default” experience, which is Docker Desktop, is a pain, due to what you described. In particular, Linux containers and Windows file permissions just don’t mix well.

Other than that, there’s three options:

1. Docker Desktop, but used from WSL 2. This seems to be the cleanest solution nowadays. Never personally used it though. Officially supported.
2. Installing Docker inside WSL 2. Configuring this correctly is a bit of a pain and not really supported AFAIK.
3. Installing Docker in a VM, using the integrated Hyper-V functionality for example. The least amount of integration, but most reliable.

markr, 10 months ago

Docker Desktop for windows (DDW) using wsl2 for hosting containers is very easy to get started with. It also integrates directly with visual studio code.

Long term you will likely want any useful container services hosted on a Linux vm rather than wsl, as wsl (and DDW) are tied to and start with your Windows user account.

ColdCreasent, 10 months ago

And WSL 2 is the “Linux within windows” if I recall. And your other recommendation is a Linux vm with dockers running inside it? I’ll give that a try if I decide to switch to dockers again instead of just a vm. My original use case was to have a downloader and vpn bundled inside one docker so the rest of the system doesn’t see the vpn connection, but decided to use a vm to accomplish it instead due to “windows+docker” issues.

PriorProject, 10 months ago (edited 10 months ago)

Others have pointed out that docker containers aren’t idiomatically like VMs and you interact with them differently. Some workflow tips:

• Don’t edit configs in containers. Mount your config files as a volume. Edit them from your host using your normal editor and restart your container when they change.
• Don’t exec into your running container and then try to install debugging tools as you need them. Use a Dockerfile to build an image that has the debugging tools you need and launch your container using that.
• In general, mess with your container less while its running. Use dockerfiles, compose, and entry point scripts to set things up in your container so it’s the way you want it on startup. While its running, just use docker logs to see what it’s doing or run the occasional debugging command via exec if you must… but do more during container-build and startup and less after it’s running. Rebuild and restart the container a lot during debugging to make your changes take effect.

The other issue in play here is that the fundamentals necessary to understand how docker containers run aren’t actually docker fundamentals. They’re:

• Networking fundamentals. The container networking stack is really configurable and really complicated.
• Volumes and config mounts are based on overlay filesystems.
• Lots of docker issues are related to complex security systems like Linux capabilities.
• All of these systems are configurable, and different docker setups use them different ways.

These things aren’t trivial to learn, a thorough understanding of these things is the difference between a junior sysadmin and a senior one, and you WILL get exposed to them when things break. But step one in learning more is definitely to recognize that the hards parts of docker are rarely docker itself. Rather, the hard parts are their own thing. Figure out what Linux system you’re struggling with and start learning about that and how docker uses it rather than narrowly focusing your research on docker itself. Anything focusing on the docker piece must necessarily gloss over the real foundations which are often very complex… so this will start you expose you to deeper material that you can assemble in your own mind into an understanding of your own specific docker setup.

sifrmoja, 10 months ago

@PriorProject @dartanjinn This is why OS containers make more sense to me. #LXC is all I use.

PriorProject, 10 months ago

I went through that phase too, but people haven’t widely adopted the idioms around immutable infrastructure for no reason. My LXC setup was more work to maintain and left me with much MUCH more upgrade uncertainty than my idiomatic/immutable container setup does. I have a deep understanding of both systems and both approaches and I would never go back to using LXC like VMs.

sifrmoja, 10 months ago

@PriorProject it's definitely more work but it's not that much. I need to set up some more automation but currently I can keep it updated with a few scripts.

Voroxpete, 10 months ago

I was in the process of writing basically this same post, but you’ve already said it very well.

Docker isn’t really a technology in and of itself; its an applicable of many of the fundamental components of Linux to create a specific result. To really understand it you have to understand the technologies it’s built from.

A recommendation I’ll throw in here for OP is How Linux Works by Brian Ward. This book is an excellent first step in really understanding those Linux fundamentals.

unscholarly_source, 10 months ago

I took a look at Dashy, I think I see the confusion. If you are looking at this article, then yes they mention Code Server, but that’s purely in the context of using Dashy in a non-docker context. But to be honest, any text editor works.

But I think that’s a red herring. That in itself has nothing to do with docker.

What you’ll need to do, once you understand the fundamentals of running docker, pull images, start a container based on an imagine, is to expose a docker volume that points to /public/conf.yaml. A docker volume ensures that the file or directory it’s mapped to in the container is available and persists outside of the container. This allows you to persist files and directories without losing them once the container stops or restarts.

Once the volume is exposed, then you can use your favorite text editor to update the dashy config file. Code Server is fine, powerful, but overkill.

But first, try getting familiar with pulling, starting stopping docker images using the cli. Gotta start there first before tinkering with docker parameters like volumes.

dartanjinn, 10 months ago

Yeah Dashy isn’t really important to me, it’s just another fun project to learn more about Docker. However, what I learned is that I don’t know shit about what I’m doing lol. It proved to be a great tool at exposing my absolute ignorance of something I thought I was getting a good grasp on.

Yeah I think I’m gonna shit can Portainer and go through that LinkedIn course someone else posted. Thanks for your insight.

unscholarly_source, 10 months ago

Portainer is definitely useful (I use it on a daily basis), but probably a bad place to start…

I started with the following progression:

1. Docker CLI
2. Docker-Compose
3. Writing my own scripts to build and manage docker-compose configs (purely optional and skippable)
4. Portainer
5. Purely optional, but in a professional setting, kubernetes and various container orchestration tools.

Good luck in your journey!

dartanjinn, 10 months ago

Docker-compose got it done. Once I learned about Volumes and using compose to pass in volumes from other instances I was able to pass in a directory with a custom yaml to the Dashy container then pass the same directory into the code-server container and both are working as I expected they should. Compose and volumes were the missing pieces. I also learned that stacks is how to use compose in Portainer. Not sure why they felt the need to change the naming but it works.

unscholarly_source, 10 months ago

That is AWESOME! Congrats!

Yes that’s right, portainer stacks equate to compose… I might be wrong, but I remember reading somewhere a while back that they (and other container orchestration tools) were not permitted to reference “Docker” or its products (including compose) due to legal and licensing restrictions by Docker.

Not to the level of Reddit, but Docker has its fair share of questionable business decisions.

redcalcium, 10 months ago

Some pointers that might help you:

You can mount the same directory in multiple containers. So you can totally have a container reading files from a directory, and access the same files on that directory from, say, a VSCode server container. Just make sure the containers both use the same UID and GID to prevent permission issues.

flubba86, 10 months ago

Sounds like you, like a lot of others, have come to docker from the perspective of “it’s like a mini virtual machine”. Maybe you’ve used VMs before, like virtualbox or VMware or EC2. Maybe you have experience with setting up a cluster of VMs, each with their own OS, own SSH client, own suite of applications, and an overlay network between them all. Maybe someone told you “you should use docker instead, it’s like mini lightweight VMs”. And you’d be right to assume this is the wrong perspective to approach docker, because it leads to the problems you have faced.

Instead, try to think of docker containers as standalone applications. They don’t contain a kernel, they don’t have SSH, no Nano or VIM, just simply the Application, in a container, with enough supporting filesystem and OS libraries to make the application work.

That perspective is what helped me to get better at docker, I know it’s not exactly answering your question, but it might help.

dartanjinn, 10 months ago

“like mini lightweight VMs”

That’s exactly how I’ve approached it cause that’s exactly how it was explained. But it’s not at all like that. Thanks for your explanation.

flubba86, 10 months ago

Same, that’s how it was explained to me too. It spent over a year learning docker the wrong way, and trying to use it as a replacement for VMs, after a coworker told me that.

NegativeLookBehind, 10 months ago

Containers are hard. This should at least get docker running without sudo: https://www.baeldung.com/linux/docker-run-without-sudo

Falmarri, 10 months ago

This is almost worse than using sudo. Because now you essentially have full sudo access without having the protections of sudo, like asking for your password

subtext, 10 months ago

Podman is supposed to be a sudo-less container manager. Though fair warning I hear it is also quite frustrating to start.

PriorProject, 10 months ago (edited 10 months ago)

Rootless podman (or docker) is a very different thing that adding yourself to the docker group. Rootless is an advanced topic that makes networking and other fundamental aspects of the container runtime work differently so it’s harder to exploit the runtime itself. Adding yourself to the docker group just gives your account permission access the docker daemon running as root… which is a much less fundamental change.

I don’t recommend beginners to mess with rootless docker or rootless podman. Rootful podman is much more straightforward (though less well documented than docker).

dartanjinn, 10 months ago

Yeah I spent a few hours with Podman before I went straight back to Docker.

macallik, 10 months ago

I've been using my library's membership to LinkedIn Learning to take a Docker Essentials course

dartanjinn, 10 months ago

I think that might be exactly what I was looking for. Thank you.

macallik, 10 months ago

Whoops, just remembered that I found the above course to be better suited for IT professionals/people with prior knowledge. Here is his course that I'm currently taking.

I find it to be much easier to follow than his prior-mentioned course

DontAskAboutUpdog, 10 months ago

Start by making a simple image and make a container of it (I started with a simple python webserver)

Once you grasp basic cli commands and the docker lingo, try pulling portainer and use its web ui.

Next step would be to customize an image.

There is a lot of information on SO, and you can ask specific questions on sites like this one. YT videos are 99% shit. Avoid.

I think docker is so stupidly awesome I nowdays dont want to do anything without it.

Oisteink, 10 months ago

You need to understand the fundamentals of how containers work. What’s inside the container is up to the creator - if you are the creator and want a package manager in there just install it. Normal way for me would be to pick a container for a system I like and add my own stuff. Find one that has what you want and add your stuff there.

Tldr: take your example and ask ChatGPT about the parts you don’t understand

nekusoul, 10 months ago

It doesn’t make any sense to me from the perspective that I’ve approached it.

I think you’ve already identified the issue. Docker is pretty “simple”, but you’ve got to approach it from the right angle or else it doesn’t make sense. Apart from suggesting the official documentation I can’t give you much advice on how to learn it because my path to understanding Docker was pretty much just trying things out and iterating on it. That said here’s a tips that could help:

• If you aren’t using Docker Compose already, you really should. Just having your entire configuration for a service in a single file really helps.
• Aside from debugging, you normally aren’t meant to run commands manually in a container. It’s best to act like every container is just a black box that simply does its thing.
• If you need to edit config files, the easiest way is to just directly on the host if you’re using bind mount volumes, or spin up a temporary container running Debian or Alpine for example that also has the Docker Volume mounted.

As @housepanther has already mentioned, building your own images is also pretty helpful since it strips a lot of the “black magic” away and teaches you how to further “mod” existing images.

housepanther, 10 months ago

I started learning docker first by how to customize an image. Since Alpine Linux is a popular light weight distro, I started with customizing it and moved from there. I also explored other people’s Dockerfiles to see how to use a Dockerfile to customize an image to containerize an app.

I found almost every YouTube howto on the subject matter very frustrating and often making the assumptions that you note. I also read the reference documentation on docker’s website. It’s not easy and it’s time consuming. I’d say I am good enough to be dangerous, not much more than that. Mostly, I’ve modified other people’s images to suite my needs

dartanjinn, 10 months ago

Thanks I’ll look into that. It doesn’t help that my introduction to Docker was using portainer so I haven’t really had much experience in the terminal outside of docker ps. I really put the cart before the horse there and am regretting it.

housepanther, 10 months ago

Hey, it’s okay. I’ve been there and done that myself. You’ll find it useful to look at both Dockerfile and docker-compose.yml files. A mistake I made early on was thinking I could replace a Dockerfile with a docker-compose.yml one. The Dockerfile itself describes how an image should be built. The docker-compose.yml file describes the environment and fetches images. It also may pass variables to the Dockerfile.