IT-SDK-Kubernetes-Basics

Ref.

• https://kind.sigs.k8s.io/
• http://kubernetesbyexample.com/
• https://kubernetes.io/docs/reference/kubectl/cheatsheet/

Infrastructure

Vagrant

# -*- mode: ruby -*-
# vi: set ft=ruby :
IMAGE_NAME = "ubuntu/focal64"

Vagrant.configure("2") do |config|
    config.vm.provider "virtualbox" do |vb|
        vb.gui = false
        vb.cpus = 2
        vb.memory = 4096
    end      
    config.vm.define "k8s-master" do |master|
        master.vm.box = IMAGE_NAME
        master.vm.hostname = "k8s-master"
        master.vm.network "public_network", bridge: "br0", mac: "0800272657FA", ip: "192.168.178.80"
    end    
    config.vm.define "k8s-node01" do |node01|
        node01.vm.box = IMAGE_NAME
        node01.vm.hostname = "k8s-node01"            
        node01.vm.network "public_network", bridge: "br0",  mac: "0800272657FB", ip: "192.168.178.81"
    end    	
end

Ansible

• Installation with Vagrant: https://kubernetes.io/blog/2019/03/15/kubernetes-setup-using-ansible-and-vagrant/

---
- hosts: all
  become: true
  tasks:
  - name: Install packages that allow apt to be used over HTTPS
    apt:
      name: "{{ packages }}"
      state: present
      update_cache: yes
    vars:
      packages:
      - apt-transport-https
      - ca-certificates
      - curl
      - gnupg-agent
      - software-properties-common

  - name: Add an apt signing key for Docker
    apt_key:
      url: https://download.docker.com/linux/ubuntu/gpg
      state: present

  - name: Add apt repository for stable version
    apt_repository:
      repo: deb [arch=amd64] https://download.docker.com/linux/ubuntu xenial stable
      state: present

  - name: Install docker and its dependecies
    apt: 
      name: "{{ packages }}"
      state: present
      update_cache: yes
    vars:
      packages:
      - docker-ce 
      - docker-ce-cli 
      - containerd.io
    notify:
      - docker status

  - name: Add vagrant user to docker group
    user:
      name: vagrant
      group: docker

  - name: Remove swapfile from /etc/fstab
    mount:
      name: "{{ item }}"
      fstype: swap
      state: absent
    with_items:
      - swap
      - none

  - name: Disable swap
    command: swapoff -a
    when: ansible_swaptotal_mb > 0

  - name: Add an apt signing key for Kubernetes
    apt_key:
      url: https://packages.cloud.google.com/apt/doc/apt-key.gpg
      state: present

  - name: Adding apt repository for Kubernetes
    apt_repository:
      repo: deb https://apt.kubernetes.io/ kubernetes-xenial main
      state: present
      filename: kubernetes.list

  - name: Install Kubernetes binaries
    apt: 
      name: "{{ packages }}"
      state: present
      update_cache: yes
    vars:
      packages:
        - kubelet 
        - kubeadm 
        - kubectl

  - name: Configure node ip
    lineinfile:
      path: /etc/default/kubelet
      line: KUBELET_EXTRA_ARGS=--node-ip={{ node_ip }}

  - name: Restart kubelet
    service:
      name: kubelet
      daemon_reload: yes
      state: restarted

  - name: Initialize the Kubernetes cluster using kubeadm
    command: kubeadm init --apiserver-advertise-address="192.168.50.10" --apiserver-cert-extra-sans="192.168.50.10"  --node-name k8s-master --pod-network-cidr=192.168.0.0/16      

  - name: Setup kubeconfig for vagrant user
    command: "{{ item }}"
    with_items:
     - mkdir -p /home/vagrant/.kube
     - cp -i /etc/kubernetes/admin.conf /home/vagrant/.kube/config
     - chown vagrant:vagrant /home/vagrant/.kube/config  

  - name: Install calico pod network
    become: false
    command: kubectl create -f https://docs.projectcalico.org/v3.4/getting-started/kubernetes/installation/hosted/calico.yaml

  - name: Generate join command
    command: kubeadm token create --print-join-command
    register: join_command
    
  - name: Copy join command to local file
    local_action: copy content="{{ join_command.stdout_lines[0] }}" dest="./join-command"

  handlers:
    - name: docker status
      service: name=docker state=started  

Cluster-Installation

swapoff -a
sudo apt-get update
sudo apt-get upgrade 
sudo apt-get install docker.io
...
sudo sh -c "echo 'deb http://apt.kubernetes.io/ kubernetes-xenial main' >> /etc/apt/sources.list.d/kubernetes.list"
sudo sh -c "curl -s https://packages.cloud.google.com/apt/doc/apt-key.gpg | apt-key add -"
...
sudo apt-get update
sudo apt-get install kubeadm=1.20.1-00 kubelet=1.20.1-00 kubectl=1.20.1-00
sudo apt-mark hold kubelet kubeadm kubectl
...
sudo sh -c "echo '192.168.178.80 k8s-master' >> /etc/hosts"
nano kubeadm-config.yaml
---------------------------
apiVersion: kubeadm.k8s.io/v1beta2
kind: ClusterConfiguration
kubernetesVersion: 1.20.1
controlPlaneEndpoint: "k8s-master:6443"
networking:
  podSubnet: 192.168.0.0/16
---------------------------
sudo kubeadm init --config=kubeadm-config.yaml --upload-certs | tee kubeadm-init.out
sudo kubeadm init --kubernetes-version 1.20.1 --pod-network-cidr 192.168.0.0/16 # Alternativ
...
mkdir -p $HOME/.kube
sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
sudo chown $(id -u):$(id -g) $HOME/.kube/config
...
kubectl apply -f https://docs.projectcalico.org/manifests/calico.yaml
kubectl get node
kubectl config use-context kubernetes-admin@kubernetes

Cluster-Updating

sudo apt-cache madison kubeadm
sudo kubeadm version
kubectl get node
...
sudo apt-mark unhold kubeadm
sudo apt-get install kubeadm=1.21.1-00
sudo apt-mark hold kubeadm
...
kubectl drain k8s-master --ignore-daemonsets # Drain node in preparation for maintenance
...
sudo kubeadm upgrade plan
sudo kubeadm upgrade apply v1.21.1
...
sudo apt-mark unhold kubelet kubectl
sudo apt-get install kubelet=1.21.1-00 kubectl=1.21.1-00
sudo apt-mark hold kubelet kubectl
...
sudo systemctl daemon-reload
sudo systemctl restart kubelet
...
kubectl uncordon k8s-master # Mark node as schedulable.

Settings

kubectl describe node | grep -i taint
kubectl taint nodes --all node-role.kubernetes.io/master-
kubectl -n kube-system describe secret default

DryRun

kubectl create deployment nginx --image=nginx --replicas=2
kubectl expose deployment nginx --type=LoadBalancer
...
kubectl create job hello --image=busybox -- echo "Hello World"
kubectl create cronjob hello --image=busybox --schedule="*/1 * * * *" -- echo "Hello World"
...
kubectl run --image=nginx -o yaml --dry-run=client > pod-defination.yaml
kubectl create deployment --image=nginx --replicas=3 -o yaml --dry-run=client > deployment-defination.yaml

ServiceTypes

• ref: https://kubernetes.io/docs/concepts/services-networking/service/
• ClusterIP: Service is reachableonly from within the cluster.
• NodePort: Service is reachable from outside the cluster.
• LoadBalancer: Service is reachable from outside the cluster (Using a cloud provider's load balancer).
• ExternalName: t.b.d.

Probes

• ref: https://kubernetes.io/docs/tasks/configure-pod-container/configure-liveness-readiness-startup-probes/

Bedeutung

• Probe: describes a health check to be performed against a container to determine whether it is alive or ready to receive traffic.
• Liveness: to know when to restart a container.
• Readiness: to know when a container is ready to start accepting traffic.
• Startup: to know when a container application has started. If such a probe is configured, it disables liveness and readiness checks until it succeeds.

Settings

• initialDelaySeconds: wait x seconds before performing the first probe.
• periodSeconds: every x seconds to perform probe.
• timeoutSeconds: wait x seconds after which the probe times out.
• successThreshold: x times to considered successful after having failed (Defaults=1).
• failureThreshold: x times to giving up after fails (Defaults=3). Giving up in case of liveness probe means restarting the container.

kind

• https://kind.sigs.k8s.io/docs/user/quick-start/#installation

curl -Lo ./kind https://kind.sigs.k8s.io/dl/v0.11.1/kind-linux-amd64
curl -Lo kind.exe https://kind.sigs.k8s.io/dl/v0.11.1/kind-windows-amd64

kind create cluster
kind create cluster --name kind-2
kind get clusters
kind delete cluster
...
kubectl cluster-info --context kind-kind

minikube

• https://minikube.sigs.k8s.io/docs/

minikube start
minikube dashboard
minikube stop		            #Halt the cluster:
minikube config set memory 16384    #Set memory limit
minikube addons list	            #Browse the catalog
minikube start -p aged --kubernetes-version=v1.16.1		#Create a second cluster
minikube delete --all		    #Delete all of the minikube