After installing (refering install_docker.sh, install_kubernetes_tools.sh), we will bootstrap the cluster on the Kube master node. Then, we will join each of the two worker nodes to the cluster, forming an actual multi-node Kubernetes cluster.

Here are the commands used:

On the Kube master node, initialize the cluster:

sudo kubeadm init --pod-network-cidr=10.244.0.0/16

That command may take a few minutes to complete. When it is done, set up the local kubeconfig:

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

Verify that the cluster is responsive and that Kubectl is working:

kubectl version

You should get Server Version as well as Client Version. It should look something like this:

Client Version: version.Info{Major:"1", Minor:"12", GitVersion:"v1.12.2", GitCommit:"17c77c7898218073f14c8d573582e8d2313dc740", GitTreeState:"clean", BuildDate:"2018-10-24T06:54:59Z", GoVersion:"go1.10.4", Compiler:"gc", Platform:"linux/amd64"}

Server Version: version.Info{Major:"1", Minor:"12", GitVersion:"v1.12.2", GitCommit:"17c77c7898218073f14c8d573582e8d2313dc740", GitTreeState:"clean", BuildDate:"2018-10-24T06:43:59Z", GoVersion:"go1.10.4", Compiler:"gc", Platform:"linux/amd64"}

The kubeadm init command should output a kubeadm join command containing a token and hash. Copy that command and run it with sudo on both worker nodes. It should look something like this:

sudo kubeadm join $some_ip:6443 --token $some_token --discovery-token-ca-cert-hash $some_hash

Verify that all nodes have successfully joined the cluster:

kubectl get nodes

Once the Kubernetes cluster is set up, we still need to configure cluster networking in order to make the cluster fully functional. We went through the process of configuring a cluster network using Flannel.

You can find more information on Flannel at the official site: https://coreos.com/flannel/docs/latest/.

Here are the commands used:

On all three nodes, run the following:

echo "net.bridge.bridge-nf-call-iptables=1" | sudo tee -a /etc/sysctl.conf sudo sysctl -p

Install Flannel in the cluster by running this only on the Master node:

kubectl apply -f https://raw.githubusercontent.com/coreos/flannel/bc79dd1505b0c8681ece4de4c0d86c5cd2643275/Documentation/kube-flannel.yml

Verify that all the nodes now have a STATUS of Ready:

kubectl get nodes

You should see all three of your servers listed, and all should have a STATUS of Ready. Get more information about a specific node:

kubectl describe node $node_name

Note: It may take a few moments for all nodes to enter the Ready status, so if they are not all Ready, wait a few moments and try again.

It is also a good idea to verify that the Flannel pods are up and running. Run this command to get a list of system pods:

kubectl get pods -n kube-system

You should have three pods with flannel in the name, and all three should have a status of Running.

In order to run and manage containers with Kubernetes, you will need to use pods.

Here are the commands used:

Create a simple pod running an nginx container:

cat << EOF | kubectl create -f -
apiVersion: v1
kind: Pod
metadata:
name: nginx
spec:
containers:
- name: nginx
image: nginx
EOF

Get a list of pods and verify that your new nginx pod is in the Running state:

kubectl get pods

Other useful commands: kubectl get pods -n kube-system

Get more information about your nginx pod:

kubectl describe pod nginx

Delete the pod:

kubectl delete pod nginx

The network functionality by contacting one pod from another pod over the virtual network. Create a deployment with two nginx pods:

cat << EOF | kubectl create -f -
apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx
  labels:
    app: nginx
spec:
  replicas: 2
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.15.4
        ports:
        - containerPort: 80
EOF

Create a busybox pod to use for testing:

cat << EOF | kubectl create -f -
apiVersion: v1
kind: Pod
metadata:
  name: busybox
spec:
  containers:
  - name: busybox
    image: radial/busyboxplus:curl
    args:
    - sleep
    - "1000"
EOF

Get the IP addresses of your pods:

kubectl get pods -o wide

Get the IP address of one of the nginx pods, then contact that nginx pod from the busybox pod using the nginx pod's IP address:

kubectl exec busybox -- curl $nginx_pod_ip

Deployments are an important tool if you want to take full advantage of the automation capabilities provided by Kubernetes. Here are the commands used:

Create a deployment:

cat <<EOF | kubectl create -f -
apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  labels:
    app: nginx
spec:
  replicas: 2
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.15.4
        ports:
        - containerPort: 80
EOF

Get a list of deployments:

kubectl get deployments

Get more information about a deployment:

kubectl describe deployment nginx-deployment

Get a list of pods:

kubectl get pods

You should see two pods created by the deployment. Delete one and check out the pods again to see how the state is maintained by deployments.

While deployments provide a great way to automate the management of your pods, you need a way to easily communicate with the dynamic set of replicas managed by a deployment. This is where services come in.

Here are the commands used:

Create a NodePort service on top of your nginx pods:

cat << EOF | kubectl create -f -
kind: Service
apiVersion: v1
metadata:
  name: nginx-service
spec:
  selector:
    app: nginx
  ports:
  - protocol: TCP
    port: 80
    targetPort: 80
    nodePort: 30080
  type: NodePort
EOF

Get a list of services in the cluster.

kubectl get svc or kubectl get service

You should see your service called nginx-service. Since this is a NodePort service, you should be able to access it using port 30080 on any of your cluster's servers. You can test this with the command:

curl localhost:30080

You should get an HTML response from nginx!