Kubernetes

• Production-Grade Container Orchestration
• History:
  • Google had a project called as borg and later omega which they use for their internal applications.
  • Google built a project based on learnings in borg and omega in golang they called it as kubernetes (k8s).
  • This project was donated to CNCF
• As of now k8s is defacto container orchestration system.

Basic Architecture

• K8s is a cluster which is one or more nodes
• K8s cluster have two types of nodes
  • Master Node(s):
    • Manage the cluster
  • Node(s):
    • Run the workloads (applications)
      
• Refer Here for master and node components
• K8s Master Node Components
  
• K8s Node Components
  
• K8s always tries to maintain a desired state.
  

K8s interfaces for extensability

• k8s when it started used to support only docker as container technology.
• K8s to call docker used to have lots of code dockershim which was part of k8s release.
• K8s has introduced a standard called CRI (Container Runtime Interface). Any container technology can be used in k8s as Container Runtime if it has CRI.
• K8s also has
  • CNI (Container Network Interface)
  • CSI (Container Storage Interface)

Options for using k8s

• Self-Hosted/On-prem:
  • Install on your own servers
• Cloud-Hosted (Managed) k8s:
  • Azure AKS
  • Google GKE
  • AWS EKS
• Single Host k8s (Developers):
  • minikube
  • kind

Installing k8s

• To Install k8s we need atleast two nodes
  • master node
  • node
• Installing k8s using kubeadm and Refer Here for installation guide
• In the class i have used Azure
• Create two vms in same network and ensure they have atleast 2 vCPUs and 2 GB of RAM.
• Installing container runtime on all nodes Refer Here
• For this installation lets use containerd

sudo apt update
sudo apt install -y curl gnupg2 software-properties-common apt-transport-https ca-certificates
sudo curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /etc/apt/trusted.gpg.d/docker.gpg
sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"
sudo apt update
sudo apt install -y containerd.io
containerd config default | sudo tee /etc/containerd/config.toml >/dev/null 2>&1
sudo sed -i 's/SystemdCgroup = false/SystemdCgroup = true/g' /etc/containerd/config.toml
sudo systemctl restart containerd
sudo systemctl enable containerd

• Now install the following kubelet, kubectl and kubeadm on all nodes

sudo apt-get update
# apt-transport-https may be a dummy package; if so, you can skip that package
sudo apt-get install -y apt-transport-https ca-certificates curl gpg
# If the directory `/etc/apt/keyrings` does not exist, it should be created before the curl command, read the note below.
# sudo mkdir -p -m 755 /etc/apt/keyrings
curl -fsSL https://pkgs.k8s.io/core:/stable:/v1.33/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:/v1.33/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

Now lets create a k8s cluster

• Refer Here
• Change the ip forward settings on all nodes

vi /etc/sysctl.conf
# see the image below and uncomment the highlighted line
sudo sysctl -p

* on the master node execute as sudo or root user

kubeadm init

• Now login into node as root user and run the kubeadm join command from above image
  
• As of now nodes are not ready due to CNI not being installed. lets install weavenet

kubectl apply -f https://github.com/weaveworks/weave/releases/download/v2.8.1/weave-daemonset-k8s.yaml

Quickly using k8s

• killerkoda