fd583d833b
When /var/lib/nydus-snapshotter is removed, containerd's BoltDB
(meta.db at /var/lib/containerd/) still holds snapshot records for
the nydus snapshotter. On the next install these stale records cause
image pulls to fail with:
"unable to prepare extraction snapshot:
target snapshot \"sha256:...\": already exists"
The failure path in core/unpack/unpacker.go:
1. sn.Prepare() → metadata layer finds the target chainID in BoltDB
→ returns AlreadyExists without touching the nydus backend.
2. sn.Stat() → metadata layer finds the BoltDB record, then calls
s.Snapshotter.Stat(bkey) on the nydus gRPC backend → NotFound
(backend was wiped).
3. The unpacker treats NotFound as a transient key-collision race and
retries 3 times; all 3 attempts hit the same dead end, and the
pull is aborted.
The commit message of 62ad0814c ("nydus: Always start from a clean
state") assumed "containerd will re-pull/re-unpack when it finds non-
existent snapshots", but that is not what happens: the metadata layer
intercepts the Prepare call in BoltDB before the backend is ever
consulted.
Fix: call cleanup_containerd_nydus_snapshots() before stopping the
nydus service (and thus before wiping its data directory) in both
install_nydus_snapshotter and uninstall_nydus_snapshotter.
The cleanup must run while the service is still up because ctr
snapshots rm goes through the metadata layer which calls the nydus
gRPC backend to physically remove the snapshot; if the service is
already stopped the backend call fails and the BoltDB record remains.
The cleanup:
- Discovers all containerd namespaces via `ctr namespaces ls -q`
(falls back to k8s.io if that fails).
- Removes containers whose Snapshotter field matches the nydus plugin
name; these become dangling references once snapshots are gone and
can confuse container reconciliation after an aborted CI run.
- Removes snapshots round by round (leaf-first) until either the list
is empty or no progress can be made (see below).
Note: containerd's GC cannot substitute for this explicit cleanup.
The image record (a GC root) references content blobs which reference
the snapshots via gc.ref labels, keeping the entire chain alive in
the GC graph even after the nydus backend is wiped.
Snapshot removal rounds
-----------------------
Snapshot chains are linear: an image with N layers produces a chain
of N snapshots, each parented on the previous. Only the current leaf
can be removed each round, so N layers require exactly N rounds.
There is no fixed round cap — the loop terminates when either the
list reaches zero (success) or a round removes nothing at all
(all remaining snapshots are actively in use by running workloads).
Active workload safety
----------------------
If active workloads still hold nydus snapshots (e.g. during a live
upgrade), no progress is made in a round and cleanup_nydus_snapshots
returns false. Both install_nydus_snapshotter and
uninstall_nydus_snapshotter gate the fs::remove_dir_all on that
return value:
- true → proceed as before: stop service, wipe data dir.
- false → stop service, skip data dir removal, log a warning.
The new nydus instance starts on the existing backend
state; running containers are left intact.
Signed-off-by: Fabiano Fidêncio <ffidencio@nvidia.com>
Made-with: Cursor
Kata Containers
Welcome to Kata Containers!
This repository is the home of the Kata Containers code for the 2.0 and newer releases.
If you want to learn about Kata Containers, visit the main Kata Containers website.
Introduction
Kata Containers is an open source project and community working to build a standard implementation of lightweight Virtual Machines (VMs) that feel and perform like containers, but provide the workload isolation and security advantages of VMs.
License
The code is licensed under the Apache 2.0 license. See the license file for further details.
Platform support
Kata Containers currently runs on 64-bit systems supporting the following technologies:
| Architecture | Virtualization technology |
|---|---|
x86_64, amd64 |
Intel VT-x, AMD SVM |
aarch64 ("arm64") |
ARM Hyp |
ppc64le |
IBM Power |
s390x |
IBM Z & LinuxONE SIE |
Hardware requirements
The Kata Containers runtime provides a command to determine if your host system is capable of running and creating a Kata Container:
$ kata-runtime check
Notes:
This command runs a number of checks including connecting to the network to determine if a newer release of Kata Containers is available on GitHub. If you do not wish this to check to run, add the
--no-network-checksoption.By default, only a brief success / failure message is printed. If more details are needed, the
--verboseflag can be used to display the list of all the checks performed.If the command is run as the
rootuser additional checks are run (including checking if another incompatible hypervisor is running). When running asroot, network checks are automatically disabled.
Getting started
See the installation documentation.
Documentation
See the official documentation including:
Configuration
Kata Containers uses a single configuration file which contains a number of sections for various parts of the Kata Containers system including the runtime, the agent and the hypervisor.
Hypervisors
See the hypervisors document and the Hypervisor specific configuration details.
Community
To learn more about the project, its community and governance, see the community repository. This is the first place to go if you wish to contribute to the project.
Getting help
See the community section for ways to contact us.
Raising issues
Please raise an issue in this repository.
Note: If you are reporting a security issue, please follow the vulnerability reporting process
Developers
See the developer guide.
Components
Main components
The table below lists the core parts of the project:
| Component | Type | Description |
|---|---|---|
| runtime | core | Main component run by a container manager and providing a containerd shimv2 runtime implementation. |
| runtime-rs | core | The Rust version runtime. |
| agent | core | Management process running inside the virtual machine / POD that sets up the container environment. |
dragonball |
core | An optional built-in VMM brings out-of-the-box Kata Containers experience with optimizations on container workloads |
| documentation | documentation | Documentation common to all components (such as design and install documentation). |
| tests | tests | Excludes unit tests which live with the main code. |
Additional components
The table below lists the remaining parts of the project:
| Component | Type | Description |
|---|---|---|
| packaging | infrastructure | Scripts and metadata for producing packaged binaries (components, hypervisors, kernel and rootfs). |
| kernel | kernel | Linux kernel used by the hypervisor to boot the guest image. Patches are stored here. |
| osbuilder | infrastructure | Tool to create "mini O/S" rootfs and initrd images and kernel for the hypervisor. |
| kata-debug | infrastructure | Utility tool to gather Kata Containers debug information from Kubernetes clusters. |
agent-ctl |
utility | Tool that provides low-level access for testing the agent. |
kata-ctl |
utility | Tool that provides advanced commands and debug facilities. |
trace-forwarder |
utility | Agent tracing helper. |
ci |
CI | Continuous Integration configuration files and scripts. |
ocp-ci |
CI | Continuous Integration configuration for the OpenShift pipelines. |
katacontainers.io |
Source for the katacontainers.io site. |
|
Webhook |
utility | Example of a simple admission controller webhook to annotate pods with the Kata runtime class |
Packaging and releases
Kata Containers is now available natively for most distributions.
General tests
See the tests documentation.
Metrics tests
See the metrics documentation.
Glossary of Terms
See the glossary of terms related to Kata Containers.