Dockershim deprecation - what does it mean for K0s?#
Back in December 2020, Kubernetes have announced the deprecation of the dockershim from version 1.24 onwards. As a consequence, k0s 1.24 and above don't support the dockershim as well.
What is dockershim and why was it deprecated?#
The dockershim is a transparent library that intercepts API calls to the kubernetes API and handles their operation in the Docker API. Early versions of Kubernetes used this shim in order to allow containers to run over docker. Later versions of Kubernetes started creating containers via the CRI (Container Runtime Interface). Since CRI has become the de-facto default runtime for Kubernetes, maintaining the dockershim turned into a heavy burden for Kubernetes maintainers, and so the decision to deprecate the built-in dockershim support came into being.
So what's going to happen to dockershim?#
Dockershim is not gone. It's only changed ownership. Mirantis has agreed to maintain dockershim (now called cri-dockerd). See: The Future of Dockershim is cri-dockerd.
From Kubernetes version 1.24 you will have the built-in possibility to run containers via CRI, but if you want to continue using docker, you are free to do so, using cri-dockerd.
In order to continue to use the Docker engine with Kubernetes v1.24+, you will have to migrated all worker nodes to use cri-dockerd.
Migrating to CRI-Dockerd#
This migration guide assumes that you've been running k0s with docker on version 1.23 and below.
The following steps will need to be done on ALL k0s' worker nodes, or single-node controllers. Basically any node that runs containers will need to be migrated using the process detailed below.
Please note that there are currently some pitfalls around container metrics when using CRI-dockerd.
Cordon and drain the node#
Get a list of all nodes (k0s is still version 1.23, which already includes the docker-shim):
sudo k0s kubectl get nodes -o wide
NAME STATUS ROLES AGE VERSION INTERNAL-IP EXTERNAL-IP OS-IMAGE KERNEL-VERSION CONTAINER-RUNTIME
ip-10-0-49-188.eu-west-1.compute.internal Ready control-plane 52m v1.28.6+k0s 10.0.49.188 <none> Ubuntu 20.04.4 LTS 5.13.0-1022-aws docker://20.10.16
ip-10-0-62-250.eu-west-1.compute.internal Ready <none> 12s v1.28.6+k0s 10.0.62.250 <none> Ubuntu 20.04.4 LTS 5.13.0-1017-aws docker://20.10.16
cordon and drain the nodes (migrate one by one):
sudo k0s kubectl cordon ip-10-0-62-250.eu-west-1.compute.internal
sudo k0s kubectl drain ip-10-0-62-250.eu-west-1.compute.internal --ignore-daemonsets
sudo k0s kubectl get nodes -o wide
NAME STATUS ROLES AGE VERSION INTERNAL-IP EXTERNAL-IP OS-IMAGE KERNEL-VERSION CONTAINER-RUNTIME
ip-10-0-49-188.eu-west-1.compute.internal Ready control-plane 56m v1.28.6+k0s 10.0.49.188 <none> Ubuntu 20.04.4 LTS 5.13.0-1022-aws docker://20.10.16
ip-10-0-62-250.eu-west-1.compute.internal Ready,SchedulingDisabled <none> 3m40s v1.28.6+k0s 10.0.62.250 <none> Ubuntu 20.04.4 LTS 5.13.0-1017-aws docker://20.10.16
Stop k0s on the node:
sudo k0s stop
Installing CRI-Dockerd#
Download the Latest cri-dockerd deb package:
cd /tmp
# Get the deb file name for ubuntu-jammy
OS="ubuntu-jammy"
PKG=$(curl -s https://api.github.com/repos/Mirantis/cri-dockerd/releases/latest | grep ${OS} | grep http | cut -d '"' -f 4)
wget ${PKG} -O cri-dockerd-latest.deb
sudo dpkg -i cri-dockerd-latest.deb
Selecting previously unselected package cri-dockerd.
(Reading database ... 164618 files and directories currently installed.)
Preparing to unpack cri-dockerd-latest.deb ...
Unpacking cri-dockerd (0.2.1~3-0~ubuntu-jammy) ...
Setting up cri-dockerd (0.2.1~3-0~ubuntu-jammy) ...
Created symlink /etc/systemd/system/multi-user.target.wants/cri-docker.service → /lib/systemd/system/cri-docker.service.
Created symlink /etc/systemd/system/sockets.target.wants/cri-docker.socket → /lib/systemd/system/cri-docker.socket.
Verify the correct version:
which cri-dockerd
/usr/bin/cri-dockerd
cri-dockerd --version
cri-dockerd 0.2.1 (HEAD)
Make sure dockershim is started:
sudo systemctl status cri-docker.service
● cri-docker.service - CRI Interface for Docker Application Container Engine
Loaded: loaded (/lib/systemd/system/cri-docker.service; enabled; vendor preset: enabled)
Active: active (running) since Wed 2022-05-25 14:27:31 UTC; 1min 23s ago
TriggeredBy: ● cri-docker.socket
Docs: https://docs.mirantis.com
Main PID: 1404151 (cri-dockerd)
Tasks: 9
Memory: 15.3M
CGroup: /system.slice/cri-docker.service
└─1404151 /usr/bin/cri-dockerd --container-runtime-endpoint fd:// --network-plugin=
Configure K0s to use dockershim#
Replace docker socket in the systemd file for cri-dockerd (the step below should be run AFTER upgrading k0s to version 1.24):
sudo sed -i -e 's_--cri-socket=docker:unix:///var/run/docker.sock_--cri-socket docker:unix:///var/run/cri-dockerd.sock_' /etc/systemd/system/k0sworker.service
sudo systemctl daemon-reload
Start k0s with cri-dockerd#
sudo k0s start
Verify the running pods via docker ps:
docker ps --format "table {{.ID}}\t{{.Names}}\t{{.State}}\t{{.Status}}\t{{.Image}}"
CONTAINER ID NAMES STATE STATUS IMAGE
1b9b4624ddfd k8s_konnectivity-agent_konnectivity-agent-5jpd7_kube-system_1b3101ea-baeb-4a22-99a2-088d7ca5be85_1 running Up 51 minutes quay.io/k0sproject/apiserver-network-proxy-agent
414758a8a951 k8s_kube-router_kube-router-qlkgg_kube-system_9a1b67bf-5347-4acd-98ac-f9a67f2db730_1 running Up 51 minutes 3a67679337a5
b81960bb304c k8s_kube-proxy_kube-proxy-tv95n_kube-system_164dc9f8-f47c-4f6c-acb7-ede5dbcd63cd_1 running Up 51 minutes quay.io/k0sproject/kube-proxy
fb888cbc5ae0 k8s_POD_kube-router-qlkgg_kube-system_9a1b67bf-5347-4acd-98ac-f9a67f2db730_0 running Up 51 minutes registry.k8s.io/pause:3.1
382d0a938c9d k8s_POD_konnectivity-agent-5jpd7_kube-system_1b3101ea-baeb-4a22-99a2-088d7ca5be85_0 running Up 51 minutes registry.k8s.io/pause:3.1
72d4a47b5609 k8s_POD_kube-proxy-tv95n_kube-system_164dc9f8-f47c-4f6c-acb7-ede5dbcd63cd_0 running Up 51 minutes registry.k8s.io/pause:3.1
On the controller, you'll be able to see the worker started with the new docker container runtime:
sudo k0s kubectl get nodes -o wide
NAME STATUS ROLES AGE VERSION INTERNAL-IP EXTERNAL-IP OS-IMAGE KERNEL-VERSION CONTAINER-RUNTIME
ip-10-0-49-188.eu-west-1.compute.internal Ready control-plane 117m v1.28.6+k0s 10.0.49.188 <none> Ubuntu 20.04.4 LTS 5.13.0-1022-aws docker://20.10.16
ip-10-0-62-250.eu-west-1.compute.internal Ready,SchedulingDisabled <none> 64m v1.28.6+k0s 10.0.62.250 <none> Ubuntu 20.04.4 LTS 5.13.0-1017-aws docker://20.10.16
Uncordon the Node#
sudo k0s kubectl uncordon ip-10-0-62-250.eu-west-1.compute.internal
node/ip-10-0-62-250.eu-west-1.compute.internal uncordoned
You should now see the node Ready for scheduling with the docker Runtime:
sudo k0s kubectl get nodes -o wide
NAME STATUS ROLES AGE VERSION INTERNAL-IP EXTERNAL-IP OS-IMAGE KERNEL-VERSION CONTAINER-RUNTIME
ip-10-0-49-188.eu-west-1.compute.internal Ready control-plane 119m v1.28.6+k0s 10.0.49.188 <none> Ubuntu 20.04.4 LTS 5.13.0-1022-aws docker://20.10.16
ip-10-0-62-250.eu-west-1.compute.internal Ready <none> 66m v1.28.6+k0s 10.0.62.250 <none> Ubuntu 20.04.4 LTS 5.13.0-1017-aws docker://20.10.16