I’m moving to a new machine soon and want to re-evaluate some security practices while I’m doing it. My current server is debian with all apps containerized in docker with root. I’d like to harden some stuff, especially vaultwarden but I’m concerned about transitioning to podman while using complex docker setups like nextcloud-aio. Do you have experience hardening your containers by switching? Is it worth it? How long is a piece of string?
I haven’t switched products but I did go through a process of hardening my containers to a degree. I did find that the hardening is limited by the authors of the software and if they have built their apps with security in mind.
I have always used docker-compose I found that easier to see what needed to be tweaked.
Some helpful links
https://docs.docker.com/docker-hub/vulnerability-scanning/
https://cheatsheetseries.owasp.org/cheatsheets/Docker_Security_Cheat_Sheet.html
I’m very much biased towards Podman, but from what I understand rootless Docker is a bit of an afterthought, while Podman has been developed from the ground up with rootless in mind. That should be reason enough.
The very few things Docker can do that Podman struggles a bit with are stuff that usually involves mounting the Docker socket in the container or other stupid things. Since you care about security, you wouldn’t do that anyway. Not to mention there’s also rootful Podman, when you need that level of access.
I’d recommend an RPM-based distro with Podman, the few times I’ve tried Podman on a deb distro, there’s always been something wonky. It’s been a while, though.
Does Podman work well when you have multiple rootless containers that you want to communicate securely in a least-privilege configuration (each container only has access to what it needs)? That is the one thing I couldn’t figure out how to do well with Podman.
Podman actually run fine on Debian 12. Though the packaged version is a bit old. Does not support podman compose command. Though podman-compose works.
Thanks. Last time I tried it was just after bookworm released, and on ARM, so it has probably got better
I’m thinking about an immutable OS with podman support first and foremost. Would you recommend Fedora CoreOS?
It’s a really solid combo, but if you’re not familiar with CoreOS I wouldn’t change both at once. Meaning migrate the services to Podman first, then switch the OS. I’ve meant to switch from Alma 9 to CoreOS a long time, but haven’t found the time.
I noticed you run Nextcloud AIO, just so you know, that’s one of those “mount the docker socket” monstrosities. I’d look into switching to the community NC image and separate containers managed yourself. AIO is easy, but if someone gets shell to the NC container, it’s basically giving root to your host.
Either way, you’re going to have trouble running AIO with Podman.
I started with rootless podman when I set up All My Things, and I have never had an issue with either maintaining or running it. Most Docker instructions are transposable, except that podman doesn’t assume everything lives as dockerhub and you always have to specify the host. I’ve run into a couple of edge cases where arguments are not 1:1 and I’ve had to dig to figure out what the argument is on podman. I don’t know if I’m actually more secure, but I feel more secure, and I really like not having the docker service running as root in the background. All in all, I think my experience with rootless podman has been better than my experience with docker, but at this point, I’ve had far more experience with podman.
Podman-compose gives me indigestion, but docker-compose didn’t exist or wasn’t yet common back when I used docker; and by the time I was setting up a homelab, I’d already settled on podman. So I just don’t use it most of the time, and wire things up by hand when necessary. Again, I don’t know whether that’s just me, or if podman-compose is more flaky than docker-compose. Podman-compose is certainly much younger and less battle-tested. So is podman but, as I said, I’ve been happy with it.
I really like running containers as separate users without that daemon - I can’t even remember what about the daemon was causing me grief; I think it may have been the fact that it was always running and consuming resources, even when I wasn’t running a container, which isn’t a consideration for a homelab. However, I’d rather deeply know one tool than kind of know two that do the same thing, and since I run containers in several different situations, using podman everywhere allows me to exploit the intimacy I wouldn’t have if I were using docker in some places and podman in others.
2¢
I make extensive use of compose in my own server so I’m assuming I’ll need to transition to systemd confs. Do you run those or do you run everything by podman CLI?
Yeah, I use systemd for the self-host stuff, but you should be able to use docker-compose files with podman-compose with no, or only minor, changes. Theoretically. If you’re comfortable with compose, you may have more luck. I didn’t have a lot of experience with docker-compose, and so when there’s hiccups I tend to just give up and do it manually, because it works just fine that way, too, and it’s easier (for me).
Hey bigdickdonkey, I recently tried and wasn’t able to shit my way through podman, there just wasn’t enough chatter and guides about it. I plan to revisit it when Debian 13 comes out, which will include podman quadlets. I also tried to get podman quadlets to work on Ubuntu 24 and got closer, but still didn’t manage and Ubuntu is squicky.
I read about true user rootless Docker and decided that was too finicky to keep up to date. It needs some annoying stuff to update, from what I could tell. I was planning on many users having their own containers, and that would have gotten annoying to manage. Maybe a single user would be an OK burden.
The podman people make a good argument for running podman as root and using userns to divvy out UIDs to achieve rootless https://www.redhat.com/en/blog/rootless-podman-user-namespace-modes but since podman is on the back burner till there’s more community and Debian 13, I applied that idea to Docker.
So I went with root Docker with the goals of:
- read only
- set user to different UID:GID for each container
- silo containers in individual Docker networks
- nothing gets /var/run/docker.sock
- cap_drop: all
- security-opt=no-new-privileges
- volumes all get tagged with :rw,noexec,nosuid,nodev,Z
Basically it’s the security best practices from this list https://cheatsheetseries.owasp.org/cheatsheets/Docker_Security_Cheat_Sheet.html
This still has risk of the Docker daemon being hacked from the container itself somehow, which podman eliminates, but it’s as close to the podman ideal I can get within my knowledge now.
Most things will run as rootless+read-only+cap_drop with minor messing. Automatic ripping machine would not, but that project is a wild ride of required permissions. Everything else has succumbed, but I’ve needed to sometimes have a “pre launch container” to do permission changes or make somewhere like /opt writable.
I would transition one app stack at a time to the best security practices, and it’s easier since you don’t need to change container managers. Hope this helps!
Quartets are a great idea but I found them very annoying in real life and ended switching back to docker.
Sad to hear for my quadlet future, do you remember what things were specifically annoying?
One of the main reason I switched to podman was its compatibility with firewalld. Haven’t used rootless docker, but podman and podman-compose gets the job done for me.
Do you run anything like fail2ban with that compatibility?
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