Derek McGowan
0b641f0099
A claimed transform was recorded but never actually left unapplied: every parsed transformer in a mount's chain was applied in full regardless of what the caller had claimed, so a shim advertising it performs "mkdir" in "format/mkdir/overlay" never got the chance to, since the manager silently applied it anyway. This predates the shim capability protocol — it was reachable before through the "format/*" annotation convention — but this series turns it into a documented, supported way for a shim to claim a transform, so a shim relying on it (at least one is: Kata's EROFS snapshotter shim, per its annotation usage) would find its claim silently ignored. A claimed transform can only be honored as a suffix of the chain: each transform's input is the previous one's output, so an outer, unclaimed transform must still be applied even when an inner one is claimed, since the inner one cannot run without it. planActivation now tracks, per mount, how much of its chain — starting from the beginning — the manager must apply itself: through the last unclaimed transform, which by construction covers every transform before it too. Applying only that prefix and returning the true, contiguous claimed suffix to the caller is what actually makes the claim meaningful. This is only observable for mounts[firstSystemMount], the one mount partially transformed by the manager and returned to the caller to finish; every earlier mount is fully internal to the manager and was, and remains, always fully transformed regardless of any claim. While changing this expression, also guard it against the case where firstSystemMount reaches len(mounts) — every mount consumed inside the manager, with no system mount left to transform — which indexes out of range today. This is a distinct, pre-existing latent panic (for example, reachable via WithTemporary combined with a transformed mount type), tracked separately from the claim-handling fix above; guarding it here only prevents a crash newly reachable by touching this line, it does not address the mount.ActivationInfo.System non-empty invariant that scenario also violates. Signed-off-by: Derek McGowan <derek@mcg.dev>
containerd is an industry-standard container runtime with an emphasis on simplicity, robustness, and portability. It is available as a daemon for Linux and Windows, which can manage the complete container lifecycle of its host system: image transfer and storage, container execution and supervision, low-level storage and network attachments, etc.
containerd is a member of CNCF with 'graduated' status.
containerd is designed to be embedded into a larger system, rather than being used directly by developers or end-users.
Announcements
Now Recruiting
We are a large inclusive OSS project that is welcoming help of any kind shape or form:
- Documentation help is needed to make the product easier to consume and extend.
- We need OSS community outreach/organizing help to get the word out; manage and create messaging and educational content; and help with social media, community forums/groups, and google groups.
- We are actively inviting new security advisors to join the team.
- New subprojects are being created, core and non-core that could use additional development help.
- Each of the containerd projects has a list of issues currently being worked on or that need help resolving.
- If the issue has not already been assigned to someone or has not made recent progress, and you are interested, please inquire.
- If you are interested in starting with a smaller/beginner-level issue, look for issues with an
exp/beginnertag, for example containerd/containerd beginner issues.
Getting Started
See our documentation on containerd.io:
To get started contributing to containerd, see CONTRIBUTING.
If you are interested in trying out containerd see our example at Getting Started.
Nightly builds
There are nightly builds available for download here.
Binaries are generated from main branch every night for Linux and Windows.
Please be aware: nightly builds might have critical bugs, it's not recommended for use in production and no support provided.
Kubernetes (k8s) CI Dashboard Group
The k8s CI dashboard group for containerd contains test results regarding the health of kubernetes when run against main and a number of containerd release branches.
Runtime Requirements
Runtime requirements for containerd are very minimal. Most interactions with
the Linux and Windows container feature sets are handled via runc and/or
OS-specific libraries (e.g. hcsshim for Microsoft).
The current required version of runc is described in RUNC.md.
There are specific features used by containerd core code and snapshotters that will require a minimum kernel version on Linux. With the understood caveat of distro kernel versioning, a reasonable starting point for Linux is a minimum 4.x kernel version.
The overlay filesystem snapshotter, used by default, uses features that were finalized in the 4.x kernel series. If you choose to use btrfs, there may be more flexibility in kernel version (minimum recommended is 3.18), but will require the btrfs kernel module and btrfs tools to be installed on your Linux distribution.
To use Linux checkpoint and restore features, you will need criu installed on
your system. See more details in Checkpoint and Restore.
Build requirements for developers are listed in BUILDING.
Supported Registries
Any registry which is compliant with the OCI Distribution Specification is supported by containerd.
For configuring registries, see registry host configuration documentation
Features
For a detailed overview of containerd's core concepts and the features it supports, please refer to the FEATURES.MD document.
Releases and API Stability
Please see RELEASES.md for details on versioning and stability of containerd components.
Downloadable 64-bit Intel/AMD binaries of all official releases are available on our releases page. Binaries are published for additional platforms as well; see Platform Support for the full list of platforms and the level of support for each.
For other architectures and distribution support, you will find that many Linux distributions package their own containerd and provide it across several architectures, such as Canonical's Ubuntu packaging.
Enabling command auto-completion
Starting with containerd 1.4, the urfave client feature for auto-creation of bash and zsh
autocompletion data is enabled. To use the autocomplete feature in a bash shell for example, source
the autocomplete/ctr file in your .bashrc, or manually like:
$ source ./contrib/autocomplete/ctr
Distribution of ctr autocomplete for bash and zsh
For bash, copy the contrib/autocomplete/ctr script into
/etc/bash_completion.d/ and rename it to ctr. The zsh_autocomplete
file is also available and can be used similarly for zsh users.
Provide documentation to users to source this file into their shell if
you don't place the autocomplete file in a location where it is automatically
loaded for the user's shell environment.
CRI
cri is a containerd plugin implementation of the Kubernetes container runtime interface (CRI). With it, you are able to use containerd as the container runtime for a Kubernetes cluster.
CRI Status
cri is a native plugin of containerd. Since containerd 1.1, the cri plugin is built into the release binaries and enabled by default.
The cri plugin has reached GA status, representing that it is:
- Feature complete
- Works with Kubernetes 1.10 and above
- Passes all CRI validation tests.
- Passes all node e2e tests.
- Passes all e2e tests.
See results on the containerd k8s test dashboard
Validating Your cri Setup
A Kubernetes incubator project, cri-tools, includes programs for exercising CRI implementations. More importantly, cri-tools includes the program critest which is used for running CRI Validation Testing.
CRI Guides
- Installing with Ansible and Kubeadm
- For Non-Ansible Users, Performing a Custom Installation Using the Release Tarball and Kubeadm
- CRI Plugin Testing Guide
- Debugging Pods, Containers, and Images with
crictl - Configuring
criPlugins - Configuring containerd
Communication
For async communication and long-running discussions please use issues and pull requests on the GitHub repo. This will be the best place to discuss design and implementation.
For sync communication catch us in the #containerd and #containerd-dev Slack channels on Cloud Native Computing Foundation's (CNCF) Slack - cloud-native.slack.com. Everyone is welcome to join and chat. Get Invite to CNCF Slack.
Join our next community meeting hosted on Zoom. The schedule is posted on the CNCF Calendar (search 'containerd' to filter).
Security audit
Security audits for the containerd project are hosted on our website. Please see the security page at containerd.io for more information.
Reporting security issues
Please follow the instructions at containerd/project
Licenses
The containerd codebase is released under the Apache 2.0 license. The README.md file and files in the "docs" folder are licensed under the Creative Commons Attribution 4.0 International License. You may obtain a copy of the license, titled CC-BY-4.0, at http://creativecommons.org/licenses/by/4.0/.
Project details
containerd is the primary open source project within the broader containerd GitHub organization.
However, all projects within the repo have common maintainership, governance, and contributing
guidelines which are stored in a project repository commonly for all containerd projects.
Please find all these core project documents, including the:
information in our containerd/project repository.
Adoption
Interested to see who is using containerd? Are you using containerd in a project? Please add yourself via pull request to our ADOPTERS.md file.