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Ansible

How to manage multiple Kubernetes nodes with Ansible.

info

Do not forget to change permissions of your ssh keys to allow Ansible to connect to them by doing the following:

sudo chmod -R 600 ~/.ssh/key_name.key

Installation​

sudo apt install software-properties-common -y && \
sudo add-apt-repository --yes --update ppa:ansible/ansible && \
sudo apt install ansible -y

Configuration​

ansible.cfg file​

If a host is reinstalled and has a different key in known_hosts, this will result in an error message until corrected. If a host is not initially in known_hosts this will result in prompting for confirmation of the key, which results in an interactive experience if using Ansible, from say, cron. You might not want this.

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Read documentation about this feature.

Create a ~/.ansible.cfg file in user's home directory:

~/.ansible.cfg
[defaults]
host_key_checking = False

Hosts file​

Path to your Ansible hosts file is: /etc/ansible/hosts.
It is where you will define your host/VM/compute/server, etc.

You can use the following hosts file configuration as example:

[workers]
my-first-worker-alias ansible_host=10.10.10.10 ansible_ssh_private_key_file=/home/ubuntu/.ssh/example-0.key
my-second-worker-alias ansible_host=10.10.10.10 ansible_ssh_private_key_file=/home/ubuntu/.ssh/example-1.key
my-third-worker-alias ansible_host=10.10.10.10 ansible_ssh_private_key_file=/home/ubuntu/.ssh/example-2.key
tip

Here, workers is the name of the group of hosts. It could be any name you want.
You can also have as many groups as you want.

Ansible action example:

ansible all -m ping # ping all hosts in the hosts file (or in the inventory)
ansible workers -m service -a "name=httpd state=restarted" # This will restart httpd on all workers.
ansible all -a "sudo apt update && sudo apt upgrade -y && sudo apt full-upgrade -y && sudo apt autoremove -y" # This will update all packages on all hosts.
tip

Argument -v is to use the verbose mode. It will print the output of the command. It is useful to know what is going on. It is not necessary to use it.

Another example of command to reboot all nodes:

ansible all -m shell -a "sudo reboot"

Playbooks​

Means the same thing as Ansible actions. It is a way to define a set of actions to be executed on a set of hosts.

info

Read documentation about Ansible playbooks.

Ansible playbooks are a way to automate the deployment of your infrastructure. It is a way to define a set of tasks that will be executed on a set of hosts.

Example command​

ansible-playbook my-playbook.yml
ansible-playbook my-playbook.yml -i hosts.txt
ansible-playbook my-playbook.yml -i hosts.txt --limit "my-first-worker-alias"

Setting up a k3s cluster using Ansible​

First, you need to install k3s on all the nodes. You can do it using the following command:

caution

Replace <MASTER_NODE_IP> and <TOKEN> by your own k3s informations.

ansible workers -v -m shell -a "curl -sfL https://get.k3s.io | K3S_URL=https://<MASTER_NODE_IP>:6443 K3S_TOKEN=<TOKEN> sh -"

For instance, to easily config. iptables on all nodes, you can use the following command:

ansible all -m shell -a "sudo iptables -A INPUT -p tcp --dport 6443 -j ACCEPT`

Hosts file example​

/etc/ansible/hosts
# My inventory file is located in /etc/ansible/hosts on the cluster.

[workers]
ampere-1 ansible_host=10.0.X.X ansible_ssh_private_key_file=~/.ssh/private.key
amd-0 ansible_host=10.0.X.X ansible_ssh_private_key_file=~/.ssh/private.key
amd-1 ansible_host=10.0.X.X ansible_ssh_private_key_file=~/.ssh/private.key