Kubeadm’s Features

Quick minimum viable cluster creation

Kubeadm is designed to have all the components you need in one place in one cluster regardless of where you are running them.

Portable

Kubeadm can be used to set up a cluster anywhere whether it's your laptop, a Raspberry Pi, or public cloud infrastructure.

Local development

As Kubeadm creates clusters with minimal dependencies and quickly, it's an ideal candidate for creating disposable clusters on local machines for development and testing needs.

Building block for other tools

Kubeadm is not just a K8s installer. It also serves as a building block for other tools like Kubespray.

Kubeadm vs kOps vs Kubespray

The Problems kubeadm Solves

How to Create a Kubernetes Cluster with kubeadm

1. Install Docker on All Three Nodes

curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
    sudo add-apt-repository 
       "deb [arch=amd64] https://download.docker.com/linux/ubuntu 
       $(lsb_release -cs) 
       Stable"
    sudo apt-get update
    sudo apt-get install -y docker-ce=18.06.1~ce~3-0~ubuntu
    sudo apt-mark hold docker-ce

sudo systemctl status docker

2. Install kubeadm, kubelet, & kubectl on All Three Nodes

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

2. cat << EOF | sudo tee /etc/apt/sources.list.d/kubernetes.list
       deb https://apt.kubernetes.io/ kubernetes-xenial main
       EOF

3. sudo apt-get update

4. sudo apt-get install -y kubelet=1.14.5-00 kubeadm=1.14.5-00 kubectl=1.14.5-00

5. sudo apt-mark hold kubelet kubeadm kubectl

3. Initiate Cluster Setup on the Master Node

1. First, we’ll initialize the control plane node and specify a network range for the pods using CIDR notation:

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

   Note: This command prints very important information which will be used later by worker nodes to join the master and form a cluster. The output should look something like this:

   'kubeadm join 10.0.1.101:6443 --token mgvt0h.3ui2w5lkjkcphc2x     --discovery-token-ca-cert-hash sha256:4e6be4e531e704e7b919a97a3b3359896b00faf3853c6d4240bf46d3a1eb990d'

2. Next, we’ll configure the kubeconfig file:

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

3. Run the kubectl version command on the Kube master node to verify it is up and running:

   > kubectl version
       Client Version: version.Info{Major:"1", Minor:"14", GitVersion:"v1.14.5", GitCommit:"0e9fcb426b100a2aea5ed5c25b3d8cfbb01a8acf", GitTreeState:"clean", BuildDate:"2019-08-05T09:21:30Z", GoVersion:"go1.12.5", Compiler:"gc", Platform:"linux/amd64"}
       Server Version: version.Info{Major:"1", Minor:"14", GitVersion:"v1.14.10", GitCommit:"575467a0eaf3ca1f20eb86215b3bde40a5ae617a", GitTreeState:"clean", BuildDate:"2019-12-11T12:32:32Z", GoVersion:"go1.12.12", Compiler:"gc", Platform:"linux/amd64"}

4. Next, we’ll check the nodes in the cluster with kubectl get nodes. At this point there should be only 1 node (the master node). Here’s an example of the expected output (don’t worry about the “NotReady” status, we’ll get to that soon!):

   > kubectl get nodes
       NAME            STATUS     ROLES    AGE   VERSION
       ip-10-0-1-101   NotReady   master   63s   v1.14.5

4. Add the Two Worker Nodes to the Cluster

1. Use kubeadm join command on both worker nodes:

   kubeadm join 10.0.1.101:6443 --token mgvt0h.3ui2w5lkjkcphc2x 
           --discovery-token-ca-cert-hash sha256:4e6be4e531e704e7b919a97a3b3359896b00faf3853c6d4240bf46d3a1eb990d

2. After running join command on both the worker nodes, go to master nodes and run the kubectl get nodes command to verify that worker nodes have joined the cluster:

   > kubectl get nodes
       NAME            STATUS     ROLES    AGE     VERSION
       ip-10-0-1-101   NotReady   master   2m41s   v1.14.5
       ip-10-0-1-102   NotReady      23s     v1.14.5
       ip-10-0-1-103   NotReady      7s      v1.14.5

5. Set up Networking for the Cluster

1. Turn on iptables bridge calls on all three nodes:

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

2. Next, run this command on only the Kube master node:

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

3. Wait a few seconds run kubectl get nodes and all the nodes should have a “Ready” status:

   > kubectl get nodes
       NAME            STATUS   ROLES    AGE     VERSION
       ip-10-0-1-101   Ready    master   4m19s   v1.14.5
       ip-10-0-1-102   Ready       2m1s    v1.14.5
       ip-10-0-1-103   Ready       105s    v1.14.5

Kubeadm Best Practices

1. Don’t use kubeadm for production clusters that require autoscaling: Generally, kubeadm should not be used for production clusters because it does not come with node autoscaling/cluster autoscaling functionality. This is because node autoscaling requires managing underlying infrastructure and hardware, which kubeadm leaves to other tools.
2. Take frequent backups of etcd: By default, kubeadm does not have a multi-etcd cluster for storing cluster state. Be sure to take regular backups of etcd in case a failure occurs.
3. Keep track of machines/nodes: Kubeadm can not turn machines off when they are not in use. As a result, you’ll need to use an external solution to track worker nodes and their resource utilization to cluster optimize cost and efficiency.