k8s_Installations

kubernetes Installation in ubuntu 20.04 for both Master & Nodes

Pre-requisites:

Create few nodes (>1)
Install docker on each node
Install CRI-dockerd on each node
Install kubeadm on each node
Make one node Master/Control Plane
Add all other nodes to the cluster
Install any CNI implementation Flannel

Configuration:

Install Docker on all the nodes

sudo apt update
curl -fsSL https://get.docker.com -o get-docker.sh && sh get-docker.sh
sudo usermod -aG docker ubuntu
exit

Install CRI-dockerd, below steps are specific to ubuntu 20.04 Refer Here

wget https://github.com/Mirantis/cri-dockerd/releases/download/v0.3.16/cri-dockerd_0.3.16.3-0.ubuntu-focal_amd64.deb
sudo dpkg -i cri-dockerd_0.3.16.3-0.ubuntu-focal_amd64.deb

Install go by executing below commands on all the nodes

sudo -i
wget https://go.dev/dl/go1.23.4.linux-amd64.tar.gz && tar -C /usr/local -xzf go1.23.4.linux-amd64.tar.gz
export PATH=$PATH:/usr/local/go/bin
git clone https://github.com/Mirantis/cri-dockerd.git
cd cri-dockerd
mkdir bin
go build -o bin/cri-dockerd
mkdir -p /usr/local/bin
install -o root -g root -m 0755 bin/cri-dockerd /usr/local/bin/cri-dockerd
cp -a packaging/systemd/* /etc/systemd/system
sed -i -e 's,/usr/bin/cri-dockerd,/usr/local/bin/cri-dockerd,' /etc/systemd/system/cri-docker.service
systemctl daemon-reload
systemctl enable cri-docker.service
systemctl enable --now cri-docker.socket
exit
exit

Next, install the following components kubeadm, kubelet and kubectl on all the nodes in the cluster being a root user

sudo apt-get update
sudo apt-get install -y apt-transport-https ca-certificates curl
curl -fsSL https://pkgs.k8s.io/core:/stable:/v1.28/deb/Release.key | sudo gpg --dearmor -o /etc/apt/keyrings/kubernetes-apt-keyring.gpg

echo 'deb [signed-by=/etc/apt/keyrings/kubernetes-apt-keyring.gpg] https://pkgs.k8s.io/core:/stable:/v1.28/deb/ /' | sudo tee /etc/apt/sources.list.d/kubernetes.list

sudo apt-get update
sudo apt-get install -y kubelet kubeadm kubectl
sudo apt-mark hold kubelet kubeadm kubectl
exit
exit

Relogin & initialize the cluster using the following command as a root user making one node Master/control-plane to create a cluster, login into a Master node and execute the following
```
sudo -i
kubeadm init --pod-network-cidr=10.244.0.0/16 --cri-socket=unix:///var/run/cri-dockerd.sock
```

OUTPUT:

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

Alternatively, if you are the root user, you can run:

  export KUBECONFIG=/etc/kubernetes/admin.conf

You should now deploy a pod network to the cluster.
Run "kubectl apply -f [podnetwork].yaml" with one of the options listed at:
  https://kubernetes.io/docs/concepts/cluster-administration/addons/

Then you can join any number of worker nodes by running the following on each as root:

kubeadm join 172.31.25.16:6443 --token sz14lp.jwkx2vy49w54fk79 \
        --discovery-token-ca-cert-hash sha256:25fe0576979b9306d911139f22c47f02240ab63731619a745b0e396ddf9fbe46

On the master node, to run kubectl as a normal user, execute the following commands as non-root user

mkdir -p $HOME/.kube
sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
sudo chown $(id -u):$(id -g) $HOME/.kube/config

Check for all the available nodes
```
kubectl get nodes
```
kuberentes needs CNI Plugin so that pod-network is enabled. Untill this is done, the DNS doesn’t work, services donot work so the status of the nodes shows ‘NotReady’. Install any CNI implementation (Flannel)
For k8s networking, the reference specification is CNI. There are many vendors who implement this Addons Installations. We are going to use flannel Let’s execute the following on master node being a normal user
```
kubectl apply -f https://github.com/flannel-io/flannel/releases/latest/download/kube-flannel.yml
```
Check if the status of all the nodes including master is ready
```
kubectl get nodes -w 
```

Autocomplete kubectl commands in command line using kubectl Cheat Sheet

source <(kubectl completion bash)
echo "source <(kubectl completion bash)" >> ~/.bashrc

After the successful installation of flannel on Master/control-plane, execute the following command on all other nodes as a root user allowing them to join the cluster

kubeadm join 172.31.25.16:6443 --token sz14lp.jwkx2vy49w54fk79 \
    --discovery-token-ca-cert-hash sha256:25fe0576979b9306d911139f22c47f02240ab63731619a745b0e396ddf9fbe46 --cri-socket "unix:///var/run/cri-dockerd.sock"

Issue ~

If you are getting the following error while joining the nodes to the cluster

[preflight] Running pre-flight checks
error execution phase preflight: [preflight] Some fatal errors occurred:
  [ERROR FileContent--proc-sys-net-bridge-bridge-nf-call-iptables]: /proc/sys/net/bridge/bridge-nf-call-iptables does not exist
[preflight] If you know what you are doing, you can make a check non-fatal with `--ignore-preflight-errors=...`
To see the stack trace of this error execute with --v=5 or higher

Resolution ~

kubeadm complains about bridge-nf-call and ip_forward if not using docker runtime #1062

Execute the following commands in worker nodes as a root

modprobe br_netfilter

echo '1' > /proc/sys/net/ipv4/ip_forward

Then, try to join the nodes to the cluster

Some useful commands –

kubectl get no

kubectl get nodes

kubectl get nodes -o wide

kubectl api-resources

kubectl api-resources | grep pod

kubectl get pods -A w

kubectl apply -f xyz.yaml

kubectl get pods -o wide

kubectl get pods <pod-name> -o yaml

kubectl describe pods <pod-name>

kubectl delete -f xyz.yaml

kubectl delete pods <pod-name>

kubectl get po -n kube-system -w

kubectl logs <pod-name>

References ~

Kubernetes Networking Model

Imperative Commands