[[improve]]

Kubernetes ist ein OpenSource System zur Automatisierung der Bereitstellung, Skalierung und Verwaltung von Container-Anwendungen (siehe [[docker|Docker]]), das ursprünglich von Google entworfen wurde. Docker hat ein integriertes Tool (Docker Swarm) zum selben Zweck, Kubernetes kann jedoch das selbe und noch viel mehr und wird ab Werk von Docker unterstützt.

Kubernetes ist deklarativ, das bedeutet man beschreibt den gewünschten Endzustand.

<box green>Ein Pod ist eine Resource eines Replicaset was eine Resourse eines Deployment ist.</box>

=====Installation (Ubuntu)=====

<box red>At least 2 cpu's and 2048 MB RAM per node are required.</box>

On all nodes

  * Edit hostname
  * Edit ''/etc/hosts'' file and add all nodes.
  * Edit ''/etc/fstab'' and uncomment SWAP partition
  * Edit ''/etc/initramfs-tools/conf.d/resume'' and uncomment swap uuid
  * Find swap unit using ''systemctl --type swap'' and mask it using ''systemctl mask xxx.swap''.

<box red>SWAP must be deactivated!</box>

todo: what about fw, selinux?

<code>
apt update && apt install apt-transport-https curl

curl -s https://packages.cloud.google.com/apt/doc/apt-key.gpg | apt-key add -

apt-add-repository "deb http://apt.kubernetes.io/ kubernetes-xenial main"

apt update && apt install -y kubelet kubeadm kubectl docker.io

systemctl enable docker
</code>

Only on master node

<code>
kubeadm init --apiserver-advertise-address 192.168.0.100 --pod-network-cidr=172.16.0.0/16

# REMEMBER JOIN TOKEN output from last command !!!!!!!!!!!!!!!!!

# when done execute as 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

# enable network addon
sudo kubectl apply -f https://raw.githubusercontent.com/coreos/flannel/master/Documentation/kube-flannel.yml
</code>

Only on nodes except master

<code>
kubeadm join 192.168.0.100:6443 --token zbdvek.v8fnw7hw8xcdxk03 --discovery-token-ca-cert-hash sha256:724601e4cd00fd78312f1fbf3726b688e894fc88f2c25962f478e546a59929c7
</code>

API Token vergessen/abgelaufen?

<code>
kubeadm token create --print-join-command
</code>

Test on master node

<code>
kubectl run my-httpd --image=httpd --port=80
kubectl get pods -l app=demo
kubectl scale deployment [deployment] --replicas 3
kubectl exec -it my-httpd -- /bin/bash
kubectl set image deployment demo nginx=1.9.1
kubectl patch pod my-httpd --patch '{}'
kubectl delete pod myhttpd
</code>

Finally autostart

<code>
systemctl start kubelet
systemctl enable kubelet
systemctl start docker
systemctl start kubelet
</code>

=====Pod=====

<code>
apiVersion: v1
kind: Pod
metadata:
  name: demo
spec:
  containers:
  - image: nginx
    name: nginx
    imagePullPolicy: Always
</code>

<code>
kubectl create -f mypod.yml
kubectl delete pod demo
</code>

=====ReplicaSet=====

Update muss manuell vorgenommen werden (downtime).

<code>
apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: demo
spec:
  replicas: 2
  selector:
    matchLabels:
      app: demo
  template:
    metadata:
      labels:
        app: demo
    spec:
      containers:
      - name: nginx
        image: nginx
        imagePullPolicy: Always
</code>

<code>
kubectl create -f myreplica.yml
kubectl delete replicaset demo
</code>

=====Deployment=====

Deployments nutzen intern replicaset und managen das rolling update von selbst.
 
<code>
apiVersion: apps/v1
kind: Deployment
metadata:
  name: demo
spec:
  replicas: 2
  selector:
    matchLabels:
      app: demo
  template:
    metadata:
      labels:
        app: demo
    spec:
      containers:
      - name: nginx
        image: nginx
        imagePullPolicy: Always
        env:
        - name: VERSION
          value: "v1"
</code>

<code>
kubectl create -f mydeployment.yml
kubectl delete deployment demo
</code>

=====Persistent Volumes=====

<code>
apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv0003
spec:
  capacity:
    storage: 5Gi
  volumeMode: Filesystem
  accessModes:
    - ReadWriteOnce
  persistentVolumeReclaimPolicy: Recycle
  storageClassName: slow
  mountOptions:
    - hard
    - nfsvers=4.1
  nfs:
    path: /tmp
    server: 172.17.0.2
</code>
=====StatefulSet=====

todo

=====Volume types=====

  * Host based
    * EmptyDir
    * HostPath
  * Block Storage
    * Amazon EBS
    * GCE Persistent Disk
    * Azure Disk
    * vSphere Volume
    * ...
  * Distributed file system
    * NFS
    * Ceph
    * Gluster
    * Amazon EFS
    * Azure File System
    * ...
  * Other
    * Flocker
    * iSCSI
    * Git Repo
    * Quobyte
    * ...
    

=====Links=====

  * [[https://youtu.be/NFApeJRXos4|Service types explained]] 
  * [[https://www.youtube.com/watch?v=d6WC5n9G_sM|Full beginner course]]
  * [[https://www.youtube.com/watch?v=S6CVIqQeJww|First steps after install]]
  * [[https://www.youtube.com/watch?v=ZxC6FwEc9WQ|Persistent volumes]]
  * [[https://www.youtube.com/watch?v=tZEKGNnvBzg|Kubectl secrets]]
  * [[https://www.youtube.com/watch?v=u948CURLDJA|Ingress NginX]]
  * [[https://www.youtube.com/watch?v=1SaPfm96lY4|The native web]]
  * [[https://www.youtube.com/watch?v=tq9ng_Nz9j8|Networking]]
  * [[https://www.youtube.com/watch?v=EQNO_kM96Mo|Application deployment tutorial video]] todo
  * [[https://stackoverflow.com/questions/69448131/kubernetes-whats-the-difference-between-deployment-and-replica-set|Difference between deployment and replicaset]]
  * [[https://github.com/derailed/k9s|K9s - Manage your Kubernetes Cluster with Style]]
  * [[https://kruschecompany.com/de/helm-kubernetes/|Die Rolle von HELM in Kubernetes]]