Ansible playbook that sets up a k3s cluster and an Elasticsearch cluster on top. Some assumptions:

• 1 master, 3 worker nodes (just remove or add worker nodes from the hosts file if you need a different number of worker nodes)
• Tested with VMs running CentOS 8 and CentOS 9 stream
• VMs have a public and a private network interface. If not, just replace the "private_ip" and "private_interface" values from the host file with the VM's public IP and network interface.
• SSH keys have been installed on VMs

I'm assuming we'll use VMs here, bare metal servers will work as well. CentOS is already installed on the servers and your public SSH key has been uploaded. Many VPS hosters allow submitting a key during creation, if not, follow these instructions. It's important that the key is installed on all servers. Make sure that TCP port 22 is accessible and that there is no firewall between the private network interfaces. The setup is flexible, you can add or remove worker nodes as needed. Also, make sure you've logged in at least once with ssh to the VMs before running the playbook so that the ssh client doesn't ask for any confirmations, or alternatively set an environment variable "ANSIBLE_HOST_KEY_CHECKING=False".

  +---+   +---+    +----------+
  | I |   | F |----| emaster  |--+
  | n |   | i |    +----------+  |
  | t |   | r |----| eworker1 |--+
  | e |---| e |    +----------+  |
  | r |   | w |----| eworker2 |--+
  | n |   | a |    +----------+  |
  | e |   | l |----| eworker3 |--+
  | t |   | l |    +----------+
  +---+   +---+    

Edit the "hosts" file, editing the server names, public IPs and private IPs to reflect your setup.

Install ansible on your computer. Each OS has a different method for doing this, on my Ubuntu it's

sudo apt install ansible

First we need to set up the VMs with a few dependencies and install k3s on it. The script

setup-elastic-cluster.sh

runs the two ansible playbooks setup-elastic.playbook and setup-k3s.playbook which configure the CentOS VMs, install k3s and then install an elastic cluster.

There are a few more environment variables that configure how ansible is run:

PATH_TO_SSH_KEY is the path to the private ssh key that should be used when connecting to hosts. Defaults to "sshkey.private".

SSH_USER is the user that should be used when connecting to hosts. Defaults to "root".

ANSIBLE_HOSTS is the path to the host inventory file that ansible should use. Defaults to "hosts".

kubectl get nodes
kubectl cluster-info
kubectl get namespaces
kubectl get endpoints -n kube-system
kubectl get pods -n kube-system
kubectl describe nodes
kubectl -n elastic-system logs -f statefulset.apps/elastic-operator
kubectl get pods -o wide
kubectl get elasticsearch

The playbooks are not good at detecting if a task is necessary and they may fail if executed repeatedly on the same VM. If you need to run a playbook again, it's best to wipe the VM first.

I haven't tested (much) how to replace a worker node. The script doesn't remove worker nodes from the kubernetes master, so there will be always a missing node which you need to take care of manually (eg. kubectl remove node $nodename). Deleting the old VM, creating a new one and running the script will work only if the new host has a different name.

Instructions for setting up k3s were taken from Install Kubernetes using k3s on CentOS 9|RHEL 9|AlmaLinux 9 by Ann Kamu.

Instructions for setting up Elastic on Kubernetes were taken from Deploy ECK in your Kubernetes cluster