29.4.1

Warning

Do not install MCR 29.4.1. This build contain an issue that can cause Swarm managers to fail and result in the loss of Swarm quorum. Upgrade instead to MCR 29.4.1.1.

Release date	Name	Upstream release
2026-MAY-13	MCR 29.4.1	Moby 29.4.1 and Docker CLI 29.4.1

Important

Due to the upgrade of containerd from 1.x to 2.x, before you upgrade from a previous MCR major release to MCR 29.4.1 you must upgrade containerd.io before you upgrade docker-ee. In the event that you have upgraded both components at the same time and some of the containers that should have restarted remain stopped, you can get them running again by restarting MCR with the systemctl restart docker command.

Changelog

MCR 29.4.1 comprises the Moby 29.4.1 upstream release.

Hotfix 29.4.1.1

Warning

Do not install MCR 29.4.1. This build contains an issue that can cause Swarm managers to fail and result in the loss of Swarm quorum. Upgrade to MCR 29.4.1.1.

The 29.4.1.1 build fixes an issue present in 29.4.1 wherein a Swarm manager failed when the leader sent a full Raft snapshot larger than approximately 4 MB to another manager:

Snapshots between approximately 4 MB and 8 MB arrived incomplete or corrupted, which prevented the receiving manager from joining or catching up with the cluster.
Snapshots larger than approximately 8 MB caused dockerd on the leader to panic with a slice bounds out of range error. Each subsequently elected leader could fail in the same way, which could result in the loss of Swarm quorum.

The issue occurs only when the leader must send its full snapshot to another manager, such as when you promote a worker to a manager, add or rebuild a manager, or bring back a manager that has fallen behind the cluster. MKE 3.x clusters are affected regardless of orchestrator type, because MKE 3.x manager nodes are Swarm managers.

Until the Swarm leader runs MCR 29.4.1.1:

Do not add, promote, or rebuild manager nodes.
Remove unused configs, secrets, and services to keep the Raft snapshot small.

If the Swarm has already lost its leader or quorum, contact Mirantis Support.

Changes specific to MCR

Fixed an issue wherein installation from FIPS channels would fail on Windows Server 2019 with a side-by-side configuration error.

Warning

Certain packages for gVisor are included in the MCR 29.4.1 release in preparation for the production release of gVisor with MCR 29.6.1. These do not yet constitute a complete implementation and thus they should not be used.

Changes from upstream

The upstream pull requests detailed in the sections that follow are those that pertain to the MCR product. For the complete list of changes and pull requests upstream, refer to the GitHub milestones.

GitHub milestones

The GitHub milestones offer full detail on the pull requests and changes as they correlate to the upstream Moby 26.0, 26.1, 27.0, 28.0, 28.1, 28.2, 28.3, 28.4, 28.5, 29.0, 28.1, and 29.2 releases.

Major component versions

Version detail for the major components that comprise MCR 29.4.1 is presented in the table below:

Component	Upstream Version	Mirantis Version
Moby	29.4.1	29.4.1m1
Docker CLI	29.4.1	29.4.1m1
containerd	2.2.3	2.2.3m1
runc	1.4.2	1.4.2m1
cri-dockerd	0.4.3	–
buildx	0.33.0	0.33.0m1
Fipster (Go runtime)	go1.26.2	go1.26.2-m1
buildkit	0.29.0	–
rootlesskit	2.3.6	–
gVisor	release-20260427.0	–
Docker Compose CLI plugin	5.1.3	5.1.3m1

Platform test detail

Platform	Kernel tested
Oracle Linux 9.7	5.14.0-611.49.1.el9_7.x86_64
Oracle Linux 8.10	4.18.0-553.123.1.el8_10.x86_64
RHEL 10.0	6.12.0-124.55.1.el10_1.x86_64
RHEL 9.7	5.14.0-611.49.1.el9_7.x86_64
RHEL 9.6	5.14.0-570.106.1.el9_6.x86_64
RHEL 8.10	4.18.0-553.120.1.el8_10.x86_64
Rocky 9.7	5.14.0-611.5.1.el9_7.x86_64
Rocky 8.10	4.18.0-553.el8_10.x86_64
SLES17 SP7	6.4.0-150700.53.40-default
Ubuntu 24.04	6.17.0-1013-aws
Ubuntu 22.04	6.8.0-1053-aws
Windows 2022 Core	10.0 20348