Docker 29 has changed its default image store for new installs(docs.docker.com) |
Docker 29 has changed its default image store for new installs(docs.docker.com) |
This seems like a really weird decision. If base images are duplicated for every image you have, that will add up quickly.
However, the tedium of the reply chain reminds me why I tend to focus most energy on internal projects rather than external open source...
Docker may have been built for a specific type of use case that most developers are familiar with (e.g. web apps backed by a DB container) but containerization is useful across so much of computing that are very different. Something that seems trivial in the python/DB space, having one or two different small duplicates of OS layers, is very different once you have 30 containers for different models+code, and then ~100 more dev containers lying around as build artifacts from building and pushing, and pulling, each at ~10GB, that the inefficient new system is just painful.
The smallest PyTorch container I ever built was 1.8GB, and that was just for some CPU-only inference endpoints, and that took several hours of yak shaving to achieve, and after a month or two of development it had ballooned back to 8GB. Containers with CUDA, or using significant other AI/ML libraries, get really big. YAGNI is a great principle for your own code when writing from scratch, but YAGNI is a bit dangerous when there's been an entire ecosystem built on your product and things are getting rewritten from scratch, because the "you" is far larger than the developer making the change. Docker's core feature has always been reusable and composable layers, so seeing it abandoned seems that somebody took YAGNI far too extreme on their own corner of the computing world.
Due to that, a careless installation of a few new dev-systems under the new docker version immediately blew up storage usage on the root-disk, while happily ignoring hundreds of gigabytes on a volume on /var/lib/docker.. because that's where it needs the storage, right? A few older systems also were upgraded but didn't, which was quite confusing at first.
Sorry for being salty, but that was a pretty hectic afternoon with those new agents trashing builds, and now we have a pretty annoying migration plan to plan for the rest. And yes yes it's just a reinstallation, but we have other things to do as well.
> The containerd image store uses more disk space than the legacy storage drivers for the same images. This is because containerd stores images in both compressed and uncompressed formats, while the legacy drivers stored only the uncompressed layers.
Why ?
This means `/var/lib/docker` is no longer "hermetic": images and container snapshots are located in `/var/lib/containerd` now.
More info about the switch: https://www.docker.com/blog/docker-engine-version-29/
To configure this directory, see https://docs.docker.com/engine/storage/containerd/.
To keep both /var/lib/{containerd,docker} in sync, I use a single ZFS dataset ("custom filesystem volume" in Incus parlance) and mount subpaths inside the container:
incus storage volume create local docker-data
incus config device add docker docker disk pool=local source=docker-data/docker path=/var/lib/docker
incus config device add docker containerd disk pool=local source=docker-data/containerd path=/var/lib/containerd
Meanwhile, the basic stuff like caching doesn't work properly.
How bad did we fall with the ship often, ship early and fix later idea? Make a major change, release it and the migration feature is experimental and not recommended.
First of all, some history; the Docker Engine was a monolith daemon that provided many services; this worked well when using Docker as a standalone solution, but when used as runtime for Kubernetes, this wasn't ideal; many components were not designed for this purpose, which meant they had to be replaced / overridden with hacks to make it work. The containerd project was created to provide a more modular runtime for the container ecosystem, providing separate subcomponents (a containerd runtime, image/content storage) for the container ecosystem to build on. It was created "from scratch" with lessons learned over the Years, providing a modern foundation.
While docker has used containerd as a runtime for many Years, it still used its own implementation for storing images ("graph-drivers"); this implementation started to show its age and had many limitations; graph-drivers have no native support for multi-platform ("multi-arch") images, no support for OCI Artifacts, and no reproducible images when pushing to different registries (among others).
Around 4 Years ago, we started to re-implement the image storage using containerd "snapshotters"; our initial goal was to provide a mostly seamless transition; add multi-arch support, but keep the UX as close as possible to the graph-drivers. Around 2 Years ago, Docker Desktop changed to using the containerd image storage (snapshotters) as a default for new installations, and Docker v29 made it the default for Linux installations.
While we kept most of the UX similar, there are some differences; when storing an image with graph-drivers, docker would pull the OCI image, extract the content (layers), and discard the (compressed) layers. While this reduced storage, it also made images non-reproducible as the image had to be re-constructed when pushing to a registry (which also resulted in slower pushes).
The containerd image storage uses a different design, where a copy of the compressed artifacts are preserved (by default); this requires more storage to keep these extra blobs, but reduces duplication and increases push performance. It was the decision containerd maintainers made early in their design process, and all containerd-based tools have used this model since the start of the containerd project.
We have a couple of roadmap items to improve this in future; some are outlined in this ticket; https://github.com/moby/moby/issues/51581, but there's other options that will become availeble through the containerd image store; support for erofs as an alternative to (tar) compressed image layers, as well as automatic garbage-collection (which would reduce the need for manually pruning content through `docker system prune` (and related commands).
(FWIW; docker still provides graph-drivers as an alternative https://docs.docker.com/engine/storage/drivers/select-storag...)
I can't believe Docker finally shit the bed. Time to replace Docker with Podman.... sigh
My reasoning is simply that I don't really want to swap out one overly complicated thing for another. I'm sure Podman is fine and amazing. But I'm just not in the IBM/Red Hat ecosystem and I have some reservations their generally a bit overly complex solutions. There's a reason IBM is involved, just saying. And as I'm not planning to use podman in production I see no reason to have it on my laptop.
As for Rancher, that seems to me a bit like moving the problem than solving it as it seems to be a for profit solution around an OSS core with its own complexity and potentially similar risks to Docker Desktop down the road.
With colima, it's all open source and easy to install/upgrade via homebrew. Nice simple wrapper around qemu. There's no UI, and I don't really miss having one. Lazydocker works fine as a TUI if you crave a UI and so do other generic docker UIs/IDEs. I mainly use docker and docker compose on the command line and that works fine for me. It has Kubernetes support as well if you need that but that's not something I use or need.
docker system prune -a -f
docker volume prune -a -f"Regularly" = when you're running out of space because of a bunch of built up old stuff.
Ref: https://docs.docker.com/reference/cli/docker/system/prune/
The 'system' context captures networks; much to my dismay, this has been a problem for no fewer than three employers. It's painfully common for things to expect the networks to persist. They don't really consume resources, so I see no reason to invite the systematic heartburn.
When? When there's disk pressure. Maybe some longer term (weekly, monthly?) to keep a lid on things. The image cache provides a benefit, no sense fighting it. At our rate, daily pruning means I might lose hours (through a week) repeatedly pulling the same images.
Just in case - I'm always amazed how many Docker users don't know about the prune command for cleaning up the caches and deleting unused container images and just slowly let their docker image cache eat their disk.
Buildkit isn't changing behavior here. Internally in docker there is a shim to make the legacy storage behave like containerd snapshotters (as well as it can, anyway--not perfect due to hard to resolve issues in the old storage). But it still kept both the compressed and uncompressed versions of images.
I'm also in the process of building a BuildKit builder, I'm seeing large improvements on the speed of exporting images. The same image that takes Docker >3 minutes to export and push takes me under a minute. https://github.com/clipper-registry/benchmarks/actions/runs/...
So much that containerization in general predates Linux, and UNIX, all the way back to System 360.
Also it got introduced into Tru64, HP-UX, BSD and Solaris, before landing into Linux.
docker image prune -a --filter "until=24h"
Inference, development cycles, any of the application domains of PyTorch that don't involve training frontier models... all of those are complicated by excessive container layers.
But mostly dev really sucks with writing out an extra 10GB for a small code change.
For some problems you might even be able to get away with single digit numbers of training points (classic example of this regime being Physics-Informed Neural Networks)
Image still ends up being like 6-8Gi tho. iirc pytorch had a hard dependency on CUDA libs which pulled in a bunch of different hardware-specific kernel binaries. The models ran on CPU and didn't even need CUDA but it was incredibly hard to remove them--there was some pytorch init code that expected the CUDA crap to exist even on CPU-only.
It still bothers me that the fastest most performant computer I have access to is almost always my laptop, and that by a considerable margin.
Someone should do some lz4 vs. ssd benchmarks across hardware to make my argument more solid and the boundaries clear.
But yes on the extreme end absolutely there's a point where lz4 stops making sense, but also most of us aren't trying to max out a 128 core postgres server or whatever.
Old docker discarded the compressed bits but kept some metadata about the the so it can at least recreate the tar.
It also recreated the manifest o push.
(As others said, compression is deterministic for the same algorithm, parameters and input data)
Also looking at block-based content store so that blocks can be deduped across images.
Tar isn't related here though, we're talking about compression not archival formats