K3s Cluster in a Weekend – Part 1 – K3s
Building a Kubernetes cluster is a great way to start learning about the power, functionality and purpose this technology provides in the modern containerization stack.
K3s is a light-weight Kuberetes compliant distribution which can run well on low powered devices and can be used on a single node cluster or it can scale up to a multi-node cluster.
This project will start with a 4 node cluster, 1 control and 3 workers. Nodes are virtual machines with 8GB of RAM and 2 – 32GB disks. The first disk will have Debian installed while the second disk will be used for cluster storage.
K3s can easily be installed on the control node with the following command, as described in the documentation
control-01:~$ curl -sfL https://get.k3s.io | sh -s - --write-kubeconfig-mode 644 --disable servicelb --token super_secret_password --node-taint CriticalAddonsOnly=true:NoExecute --bind-address 10.33.0.100
A couple of additional flags are passed to the install script then described in the K3s Quick start guide. Detail on the configuration options can be found on on https://docs.k3s.io/cli/server.
Briefly,
—write-kubeconfig-mode 644 will allow non-root users to read /etc/rancher/k3s/k3s.yaml, the k3s configuration file.
—disable servicelb is used to disable the ServiceLB package. Later on, a different load balance manager, MetalLB will be installed.
—token supersecretpassword defines the password that will be used to connect agent nodes to the server.
—node-taint CriticalAddonsOnly=true:NoExecute creates a node taint that prevents pods to running on the control-plane node unless a tolerance value of “CriticalAddonsOnly” exits. A further explanation would be,
By default, server nodes will be schedulable and thus your workloads can get launched on them. If you wish to have a dedicated control plane where no user workloads will run, you can use taints. https://docs.k3s.io/datastore/ha#2-launch-server-nodes
Setup an env variable on control node to simplify using kubectl.
control-01:~$ echo "KUBECONFIG=/etc/rancher/k3s/k3s.yaml" >> /etc/environment
Install K3s as an Agent on the worker nodes, worker01-03. K3S_URL is the IP of the control node.
worker-01:~$ curl -sfL https://get.k3s.io | K3S_URL=https://10.33.0.100:6443 K3S_TOKEN=super_secret_password sh -
Label each worker to organize the nodes in the cluster.
control-01:~$ kubectl label nodes k3s-worker-01 kubernetes.io/role=worker
The cluster should be operational at this point. We can check the status of the nodes with kubectl get nodes --show-labels.