Debian has work-in-progress packages for Kubernetes, which work well enough enough for a testing and learning environement. Bootstraping a cluster with the kubeadm deployer with these packages is not that hard, and is similar to the upstream kubeadm documentation
Install necessary packages in a VM
Install a throwaway VM with Vagrant.
apt install vagrant vagrant-libvirt
vagrant init debian/testing64
Bump the RAM and CPU of the VM, Kubernetes needs at least 2 gigs and 2 cores.
awk -i inplace '1;/^Vagrant.configure\("2"\) do \|config/ {print " config.vm.provider :libvirt do |vm| vm.memory=2048 end"}' Vagrantfile
awk -i inplace '1;/^Vagrant.configure\("2"\) do \|config/ {print " config.vm.provider :libvirt do |vm| vm.cpus=2 end"}' Vagrantfile
Start the VM, login, update the package index.
vagrant up
vagrant ssh
sudo apt update
Install a container engine, here we use docker.io, we could also use containerd (both are packaged in Debian) or cri-o.
sudo apt install --yes --no-install-recommends docker.io curl
Install kubernetes binaries. This will install kubelet, the system service which will manage the containers, and kubectl the user/admin tool to manage the cluster.
sudo apt install --yes kubernetes-{node,client} containernetworking-plugins
Although it is not technically mandatory, we will use kubeadm, the most popular installer to create a Kubernetes cluster. Kubeadm is not packaged in Debian, we have to download an upstream binary.
wget https://dl.k8s.io/v1.20.5/kubernetes-server-linux-amd64.tar.gz
sha512sum kubernetes-server-linux-amd64.tar.gz
28529733bf34f5d5b72eabe30a81df98cc7f8e529590f807745cd67986a2c5c3eb86cebc7ecbcfc3df3c50416306e5d150948f2483933ea46c2aebaeb871ea8f kubernetes-server-linux-arm64.tar.gz
sudo tar --directory=/usr/local/sbin --strip-components 3 -xaf kubernetes-server-linux-amd64.tar.gz kubernetes/server/bin/kubeadm
sudo chmod +x /usr/local/sbin/kubeadm
sudo kubeadm version
kubeadm version: &version.Info{Major:"1", Minor:"20", GitVersion:"v1.20.5", GitCommit:"6b1d87acf3c8253c123756b9e61dac642678305f", GitTreeState:"clean", BuildDate:"2021-03-18T01:08:27Z", GoVersion:"go1.15.8", Compiler:"gc", Platform:"linux/amd64"}
Add a kubelet systemd unit:
RELEASE_VERSION="v0.4.0"
curl -sSL "https://raw.githubusercontent.com/kubernetes/release/${RELEASE_VERSION}/cmd/kubepkg/templates/latest/deb/kubelet/lib/systemd/system/kubelet.service" | sudo tee /etc/systemd/system/kubelet.service
sudo systemctl enable kubelet
and a default config file for kubeadm
RELEASE_VERSION="v0.4.0"
sudo mkdir -p /etc/systemd/system/kubelet.service.d
curl -sSL "https://raw.githubusercontent.com/kubernetes/release/${RELEASE_VERSION}/cmd/kubepkg/templates/latest/deb/kubeadm/10-kubeadm.conf" | sudo tee /etc/systemd/system/kubelet.service.d/10-kubeadm.conf
finally we need to help kubelet find the components needed for container networking
echo 'KUBELET_EXTRA_ARGS="--cni-bin-dir=/usr/lib/cni"' | sudo tee /etc/default/kubelet
Create a cluster
Initialize a cluster with kubeadm: this will download container images for the Kubernetes control plane (= the brain of the cluster), and start the containers via the kubelet service. Yes a good part of Kubernetes itself run in containers.
sudo kubeadm init --pod-network-cidr=10.244.0.0/16
...
...
Your Kubernetes control-plane has initialized successfully!
To start using your cluster, you need to run the following as a regular user:
mkdir -p $HOME/.kube
sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
sudo chown $(id -u):$(id -g) $HOME/.kube/config
Follow the instructions from the kubeadm output, and verify you have a single node cluster, with the status NotReady.
kubectl get nodes
NAME STATUS ROLES AGE VERSION
testing NotReady control-plane,master 9m9s v1.20.5
At that point you should also have a bunch of containers running on the node:
sudo docker ps --format '{{.Names}}'
k8s_kube-apiserver_kube-apiserver-testing_kube-system_2711c230d39ccda1e74d1d6386a05cee_0
k8s_POD_kube-apiserver-testing_kube-system_2711c230d39ccda1e74d1d6386a05cee_0
k8s_etcd_etcd-testing_kube-system_4749b1bca3b1a73fd09c8e299d7030fe_0
k8s_POD_etcd-testing_kube-system_4749b1bca3b1a73fd09c8e299d7030fe_0
...
The kubelet service also needs an external network plugin to get the cluster in Ready state.
sudo systemctl status kubelet
...
Mar 28 09:28:43 testing kubelet[9405]: E0328 09:28:43.958059 9405 kubelet.go:2188] Container runtime network not ready: NetworkReady=false reason:NetworkPluginNotReady message:docker: network plugin is not ready: cni config uninitialized
Let’s add that network plugin. Download the flannel network plugin definition, and schedule flannel to run on all nodes of your cluster:
wget https://raw.githubusercontent.com/coreos/flannel/master/Documentation/kube-flannel.yml
kubectl apply --filename=kube-flannel.yml
After a dozen of seconds your node should be in ready status.
kubectl get nodes
NAME STATUS ROLES AGE VERSION
testing Ready control-plane,master 16m v1.20.5
Deploy a test application
Our node is now in Ready status, but we cannot run application on it, since we only have a master node, an administrative node which by default cannot run user applications.
kubectl describe node testing | grep ^Taints
Taints: node-role.kubernetes.io/master:NoSchedule
Let’s allow node testing to run user applications:
kubectl taint node testing node-role.kubernetes.io/master-
Deploy a nginx container:
kubectl run my-nginx-pod --image=docker.io/library/nginx --port=80 --labels="app=http-content"
Create a Kubernetes service to access this pod externally:
cat service.yaml
apiVersion: v1
kind: Service
metadata:
name: my-k8s-service
spec:
type: NodePort
ports:
- port: 80
nodePort: 30000
selector:
app: http-content
kubectl create --filename service.yaml
Access the service via IP adress:
curl 192.168.121.63:30000
...
Thank you for using nginx.
Notes
I will try to get this blog post in a Debian Wiki article, or maybe in the kubernetes-node documentation. Blog posts deprecate and disappear, wiki and project docs live longer.
