Kubernetes

Website kubernetes.io Type Cluster management software and container orchestration Repository https://github.com/kubernetes/kubernetes

-What is Kubernetes

Architecture

sites :

  1. https://thenewstack.io/kubernetes-an-overview/
  2. https://x-team.com/blog/introduction-kubernetes-architecture/
  3. https://medium.com/@abhaydiwan/kubernetes-introduction-and-twelve-key-features-cdfe8a1f2d21
  4. https://medium.com/jorgeacetozi/kubernetes-master-components-etcd-api-server-controller-manager-and-scheduler-3a0179fc8186

I] Kubernetes Master - Kubernetes Masters act as the control unit for a cluster. - Manages its workload and directs communication across the system. - A cluster needs 1 or more Masters to run

II] Kubernetes Nodes

- The Node, also known as Worker or Minion
- Kubernetes Nodes actually run the workloads(containers).
- Kubernetes needs at least 1 node to run.
- In small setups, the node and the master can be the same.

K8s Basics

Services

https://medium.com/google-cloud/kubernetes-nodeport-vs-loadbalancer-vs-ingress-when-should-i-use-what-922f010849e0

  1. ClusterIP
    • A ClusterIP service is the default Kubernetes service.
    • Service gets virtual IP which only used to communicate within the cluster.
    • It gives you a service inside your cluster that other apps inside your cluster can access. There is no external access.
  2. NodePort
    • Derives properties of ClusterIP.
    • Makes a service accessible from outside the cluster
    • In addition, it gets port from range 30000-32767 mapped with all nodes in cluster

Tools

  1. Kubeadm
    • A administration tool for setting up and managing kubernetes clusters. Kubeadm runs on the Kubernetes host.
  2. Kubectl
    • The command line interface for interacting with a Kubernetes clusters

Kubernetes Features

  1. Automatic binpacking Automatically places containers based on their resource requirements and other constraints, while not sacrificing availability. Mix critical and best-effort workloads in order to drive up utilization and save even more resources.

  2. Horizontal scaling Scale your application up and down with a simple command, with a UI, or automatically based on CPU usage.

  3. Automated rollouts and rollbacks Kubernetes progressively rolls out changes to your application or its configuration, while monitoring application health to ensure it doesn’t kill all your instances at the same time. If something goes wrong, Kubernetes will rollback the change for you. Take advantage of a growing ecosystem of deployment solutions.

  4. Storage orchestration Automatically mount the storage system of your choice, whether from local storage, a public cloud provider such as GCP or AWS, or a network storage system such as NFS, iSCSI, Gluster, Ceph, Cinder, or Flocker.

  5. Self-healing Restarts containers that fail, replaces and reschedules containers when nodes die, kills containers that don’t respond to your user-defined health check, and doesn’t advertise them to clients until they are ready to serve.

  6. Service discovery and load balancing No need to modify your application to use an unfamiliar service discovery mechanism. Kubernetes gives containers their own IP addresses and a single DNS name for a set of containers, and can load-balance across them.

  7. Secret and configuration management Deploy and update secrets and application configuration without rebuilding your image and without exposing secrets in your stack configuration.

  8. Batch execution In addition to services, Kubernetes can manage your batch and CI workloads, replacing containers that fail, if desired.

Creating a single master cluster with kubeadm

Sites :

  1. https://kubernetes.io/docs/setup/independent/create-cluster-kubeadm/
  2. https://kubernetes.io/docs/tasks/tools/install-kubeadm/

Steps :

  1. vim /etc/yum.repos.d/kubernetes.repo
    • Add this [kubernetes] name=Kubernetes baseurl=https://packages.cloud.google.com/yum/repos/kubernetes-el7-x86_64 enabled=1 gpgcheck=1 repo_gpgcheck=1 gpgkey=https://packages.cloud.google.com/yum/doc/yum-key.gpg https://packages.cloud.google.com/yum/doc/rpm-package-key.gpg
  2. setenforce 0
  3. yum install -y kubelet kubeadm kubectl

  4. systemctl enable kubelet && systemctl start kubelet

  5. vim /etc/sysctl.d/k8s.conf
    • Add this net.bridge.bridge-nf-call-ip6tables = 1 net.bridge.bridge-nf-call-iptables = 1
  6. sysctl –system

Demo Using Ansible

	- hostnamectl set-hostname Master
	- hostnamectl set-hostname Node
  1. yum install ansible
  2. git clone https://github.com/kairen/kubeadm-ansible.git
  3. cd kubeadm-ansible/
  4. vim hosts.ini
    • Edit Master and Node IP address
  5. ansible-playbook site.yaml
  6. ansible-playbook site.yaml –limit @/root/kubeadm-ansible/site.retry
  1. To set up the kubernetes master. ```
    • kubeadm init –service-cidr 10.96.0.0/12 –kubernetes-version v1.11.0 –pod-network-cidr “10.244.0.0/16” –token b0f7b8.8d1767876297d85c –apiserver-advertise-address 10.10.121.222 ```
  2. mkdir -p $HOME/.kube
  3. sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
  4. sudo chown $(id -u):$(id -g) $HOME/.kube/config
  5. Deploy a pod network to the cluster (flannel)
    • kubectl apply -f https://raw.githubusercontent.com/coreos/flannel/master/Documentation/kube-flannel.yml
  1. You can now join any number of machines by running the following on each node ```
    • kubeadm join 10.10.X.222:6443 –token b0f7b8.8d1767876297d85c –discovery-token-ca-cert-hash sha256:f4a0f891e5e5afde7c273d38b8762c2915e29a8ee807fadeea5382bc8c90407b 
                                OR
    • kubeadm join 10.10.X.222:6443 –token b0f7b8.8d1767876297d85c –discovery-token-unsafe-skip-ca-verification ```

Demo Using Manual Commands

– Kubernetes Installation on both Master and Node

  1. Configure Hosts
    • vim /etc/hosts 10.0.15.10 k8s-master 10.0.15.21 node01 10.0.15.22 node02
  2. Disable SELinux
    • setenforce 0
    • sed -i –follow-symlinks ‘s/SELINUX=enforcing/SELINUX=disabled/g’ /etc/sysconfig/selinux
  3. Enable br_netfilter Kernel Module
    • modprobe br_netfilter
    • echo ‘1’ > /proc/sys/net/bridge/bridge-nf-call-iptables
  4. Disable SWAP
    • swapoff -a
    • edit vim /etc/fstab Comment the swap line UUID
  5. Install Docker CE
    • yum install -y yum-utils device-mapper-persistent-data lvm2
    • yum-config-manager –add-repo https://download.docker.com/linux/centos/docker-ce.repo
    • yum install -y docker-ce
  6. Install Kubernetes

    • cat «EOF > /etc/yum.repos.d/kubernetes.repo [kubernetes] name=Kubernetes baseurl=https://packages.cloud.google.com/yum/repos/kubernetes-el7-x86_64 enabled=1 gpgcheck=1 repo_gpgcheck=1 gpgkey=https://packages.cloud.google.com/yum/doc/yum-key.gpg https://packages.cloud.google.com/yum/doc/rpm-package-key.gpg EOF

    • yum install -y kubelet kubeadm kubectl
    • sudo reboot
    • systemctl start docker && systemctl enable docker
    • systemctl start kubelet && systemctl enable kubelet
  7. Change the cgroup-driver
    • Check docker cgroup using the docker info command.
      • docker info grep -i cgroup
    • sed -i ‘s/cgroup-driver=systemd/cgroup-driver=cgroupfs/g’ /etc/systemd/system/kubelet.service.d/10-kubeadm.conf
    • systemctl daemon-reload
    • systemctl restart kubelet

  1. Creating Kubernetes Cluster

    1. To set up the kubernetes master
      • kubeadm init –apiserver-advertise-address=10.0.15.10 –pod-network-cidr=10.244.0.0/16

Note : –apiserver-advertise-address = determines which IP address Kubernetes should advertise its API server on. –pod-network-cidr = specify the range of IP addresses for the pod network. We’re using the ‘flannel’ virtual network. If you want to use another pod network such as weave-net or calico, change the range IP address.

2. Now in order to use Kubernetes
	- mkdir -p $HOME/.kube
	- sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
	- sudo chown $(id -u):$(id -g) $HOME/.kube/config

3. Deploy the flannel network to the kubernetes cluster
	- kubectl apply -f https://raw.githubusercontent.com/coreos/flannel/master/Documentation/kube-flannel.yml

- kubectl cluster-info
- kubectl get nodes 
- kubectl get pods --all-namespaces
- kubectl delete node name

  1. Joining Node to Cluster

    1. This command is used to get join node information if u missed ```
      • kubeadm token create –print-join-command ```
    2. You can now join any number of machines by running the following on each node ```
      • kubeadm join 10.10.121.222:6443 –token b0f7b8.8d1767876297d85c –discovery-token-ca-cert-hash sha256:f4a0f891e5e5afde7c273d38b8762c2915e29a8ee807fadeea5382bc8c90407b 
        
                       OR

           - kubeadm join 10.10.121.222:6443 --token b0f7b8.8d1767876297d85c --discovery-token-unsafe-skip-ca-verification
    • kubectl get nodes
    • kubectl delete node name ``` ?4zQc}syHy5XN[he

  2. Creating Deployment

sites : 1. https://www.howtoforge.com/tutorial/centos-kubernetes-docker-cluster/ (command) 2. https://kubernetes.io/docs/concepts/workloads/controllers/deployment/ (file)

Steps :

1. Login to the 'k8s-master' server and create new deployment named 'nginx'  ```
	- kubectl create deployment nginx --image=nginx
					OR
	- kubectl create -f <file-name>  					

	file-name = nginx-deployment.yaml		

		apiVersion: apps/v1
		kind: Deployment
		metadata:
		  name: nginx-deployment
		  labels:
		    app: nginx
		spec:
		  replicas: 3
		  selector:
		    matchLabels:
		      app: nginx
		  template:
		    metadata:
		      labels:
		        app: nginx
		    spec:
		      containers:
		      - name: nginx
		        image: nginx:1.7.9
		        ports:
		        - containerPort: 80 ```

2. To see details of the 'nginx' deployment sepcification ```
-  kubectl describe deployment nginx
- kubectl get deployments
- kubectl get deployment <deployment-name> -o yaml
- kubectl delete deployment <deployment_name>

- kubectl get pods
- kubectl get pods --all-namespaces
- kubectl get pods -o wide (along with IP address)
- kubectl delete pod <pod_name>

			
4. Creating Service 

sites : 
	1. https://www.howtoforge.com/tutorial/centos-kubernetes-docker-cluster/	(command) 
	2. https://kubernetes.io/docs/concepts/services-networking/service/			(file)

Steps :

	1. Next, expose the nginx pod accessible via the internet. And we need to create new service NodePort for this.

	- kubectl create service nodeport nginx --tcp=80:80 ```

2. From the 'k8s-master' server run the curl command below. ```
	- curl node-name : service-port ```

3. The Nginx Pod has now been deployed under the Kubernetes cluster and it's accessible via the internet.
	http://node-ip:service-port/ ```
- kubectl get svc
- kubectl describe services/<service-name> ```
  1. Scaling Current Deployment

sites : 1. https://kubernetes.io/docs/tutorials/kubernetes-basics/scale/scale-interactive/ 2. https://cloud.google.com/kubernetes-engine/docs/how-to/scaling-apps

Steps :

1. scale the Deployment to 4 replicas. Followed by the deployment type, name and desired number of instances: ```
	- kubectl scale deployments/<deployment-name> --replicas=4 ```
2. Scale Down ```
	- kubectl scale deployments/<deployment-name> --replicas=2 ```

3. check docker container scaling or not. Remove 1 docker container and it will get scaled ```
- docker rm container-id
- kubectl get deployments
- kubectl get pods -o wide
- kubectl describe deployments/<deployment-name> ```
  1. Autoscaling Deployments

sites : 1. https://cloud.google.com/kubernetes-engine/docs/how-to/scaling-apps

steps :

1. autoscale Deployments based on CPU utilization of Pods using kubectl autoscale
	- kubectl autoscale deployment <deployment-name> --max 6 --min 4 --cpu-percent 50

2. To see a specific HorizontalPodAutoscaler object in your cluster
	- kubectl get hpa [HPA_NAME]

3. To see the HorizontalPodAutoscaler configuration
	- kubectl get hpa [HPA_NAME] -o yaml

4. To see a detailed description of a specific HorizontalPodAutoscaler object in the cluster
	- kubectl describe hpa [HPA_NAME]

5. To delete a HorizontalPodAutoscaler object
	- kubectl delete hpa [HPA_NAME]
  1. Web UI (Dashboard)

sites :

1. https://kubernetes.io/docs/tasks/access-application-cluster/web-ui-dashboard/#deploying-the-dashboard-ui
2. https://github.com/kubernetes/dashboard/wiki/Accessing-Dashboard---1.7.X-and-above
3. https://stackoverflow.com/questions/46664104/how-to-sign-in-kubernetes-dashboard

steps :

1. Deploying the Dashboard UI
	- kubectl create -f https://raw.githubusercontent.com/kubernetes/dashboard/master/src/deploy/recommended/kubernetes-dashboard.yaml

2. Accessing the Dashboard UI
	- kubectl proxy OR

3. Edit kubernetes-dashboard service.
	- kubectl -n kube-system get service kubernetes-dashboard
	- kubectl -n kube-system edit service kubernetes-dashboard
		- Change type: ClusterIP to type: NodePort and save file

4. Create kube-dashboard-access.yaml file
	- vim kube-dashboard-access.yaml
	
		apiVersion: rbac.authorization.k8s.io/v1beta1
		kind: ClusterRoleBinding
		metadata:
		  name: kubernetes-dashboard
		  labels:
		    k8s-app: kubernetes-dashboard
		roleRef:
		  apiGroup: rbac.authorization.k8s.io
		  kind: ClusterRole
		  name: cluster-admin
		subjects:
		- kind: ServiceAccount
		  name: kubernetes-dashboard
		  namespace: kube-system

	- kubectl create -f kube-dashboard-access.yaml

5. Run on
	- kubectl -n kube-system get service kubernetes-dashboard 
	- https://<master-ip>:<service-port>

6, Sign in with Token  ```
- kubectl -n kube-system get secret
 	- kubectl -n kube-system describe secret <name>  			(kubernetes-dashboard-token-7vwwp) ```

– CaaS –

Sites :

  1. https://www.1and1.com/digitalguide/server/know-how/caas-container-as-a-service-service-comparison/
  2. https://www.gartner.com/doc/3666417/container-services-public-cloud
  3. https://blog.docker.com/2016/02/containers-as-a-service-caas/
kubeadm join 10.10.121.222:6443 --token b0f7b8.8d1767876297d85c --discovery-token-ca-cert-hash sha256:17ccb41872fb3a405df498b3d10acdd2fc47787ee541b58f87e8e71933134c65

kubeadm join 10.10.121.222:6443 --token b0f7b8.8d1767876297d85c --discovery-token-ca-cert-hash sha256:90bec7aa30b4b0fe5709bbb2cc46f49fa356b18eb381e52726b89d2ea59358b1

kubeadm join 10.10.121.222:6443 --token b0f7b8.8d1767876297d85c --discovery-token-ca-cert-hash sha256:bdc0c2d38048641916d9b49bc5795eaa9129ebe704722c23832c9d8edb147a1c

https://www.server-world.info/en/note?os=CentOS_7&p=kubernetes https://www.server-world.info/en/note?os=CentOS_7&p=kubernetes&f=3 https://www.server-world.info/en/note?os=CentOS_7&p=docker&f=1

  1. What is Kubernetes?
  1. How is Kubernetes related to Docker?