Introduction to Kubernetes Cluster

Kubernetes

Kubernetes is an open-source system for automating deployment, scaling, and management of containerized applications.

Installation

Distro: Ubuntu 16.04
Servers: Master
	Node Server 1
	Node Server 2

Disable the swap file on all servers

sudo swapoff -a

Remove any matching reference found in /etc/fstab

Install the Docker

apt-get update

apt-get install -y apt-transport-https ca-certificates curl software-properties-common

curl -fsSL https://download.docker.com/linux/ubuntu/gpg | apt-key add -

add-apt-repository "deb https://download.docker.com/linux/$(. /etc/os-release; echo "$ID") $(lsb_release -cs) stable"

apt-get update && apt-get install -y docker-ce=$(apt-cache madison docker-ce | grep 17.03 | head -1 | awk '{print $3}')

Install Kubernetes packages

You will install these packages on all of your machines:

kubeadm: the command to bootstrap the cluster. kubelet: the component that runs on all of the machines in your cluster and does things like starting pods and containers. kubectl: the command line util to talk to your cluster.

apt-get update && apt-get install -y apt-transport-https curl

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

cat <<EOF >/etc/apt/sources.list.d/kubernetes.list
deb http://apt.kubernetes.io/ kubernetes-xenial main
EOF	

apt-get update

apt-get install -y kubelet kubeadm kubectl kubernetes-cni

Create the cluster

We need to create the cluster by initiating the master with kubeadm. Only do this on the master node.

The Kubernetes master is responsible for maintaining the desired state for your cluster.

sudo kubeadm init --pod-network-cidr=172.16.0.0/16

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

Login to the other two nodes which are the worker nodes and use the token to join them to the master node. The worker nodes in a cluster are the machines (VMs, physical servers, etc) that run your applications and cloud workflows.

kubeadm join <ip>:6443 --token <token key> --discovery-token-ca-cert-hash sha256:<key>

Install networking

Only on master execute the following

Weave NET

kubectl apply -f "https://cloud.weave.works/k8s/net?k8s-version=$(kubectl version | base64 | tr -d '\n')"
curl -SL "https://cloud.weave.works/k8s/net?k8s-version=$(kubectl version | base64 | tr -d '\n')&env.IPALLOC_RANGE=172.16.0.0/16" | kubectl apply -f -

Creating Pods, Deployments and Services

Pod

A Kubernetes Pod represents a running process on your cluster. A pod is a group of one or more containers, with shared storage/network, and a specification for how to run the containers.

Example Create a pod.yaml

apiVersion: v1
kind: Pod
metadata:
  name: nginx
spec:

  restartPolicy: Always

  volumes:
  - name: shared-data
    emptyDir: {}

  containers:

  - name: nginx-container
    image: nginx
    volumeMounts:
    - name: shared-data
    mountPath: /usr/share/nginx/html

kubectl create -f pod.yaml

Deployment

A kubernetes Deployment manages creating Pods by means of ReplicaSets.

ReplicaSet is the next-generation Replication Controller.A ReplicaSet ensures that a specified number of pod replicas are running at any given time.

create a 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

kubectl create -f deployment.yaml

Replicas can be changed either by editing the deployment or using scale.

kubectl edit deployment nginx
	
kubectl scale --replicas=3 deployment/nginx

Service

A Kubernetes Service is an abstraction which defines a logical set of Pods and a policy by which to access them. . The set of Pods targeted by a Service is determined by a Label Selector

create service.yaml file

kind: Service
apiVersion: v1
metadata:
  name: nginx-service
spec:
  selector:
    app: nginx
  ports:
  - protocol: TCP
    port: 80
    targetPort: 9376

kubectl create -f service.yaml

Sources

https://kubernetes.io/docs/