A simple Ansible playbook for yum based distributions that installs Docker & K8s and initialises the k8s cluster (with Flannel as a network add-on)

k8s-init-play.yml

--- 
- hosts: k8s_master,k8s_workers
  become: true
  remote_user: ansible
  tasks:

  # Docker installation

  - name: Install helper packages
    yum:
      name: yum-utils,device-mapper-persistent-data,lvm2
      state: latest
  - name: Set up stable Docker repo
    command: 
      cmd: yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo
      creates: /etc/yum.repos.d/docker-ce.repo
  - name: Install Docker Engine
    yum:
      name: docker-ce,docker-ce-cli,containerd.io
      state: latest
  - name: Start Docker service
    service:
      name: docker
      state: started
  
  # K8s installation
  
  - name: Get kubernetes.repo info
    register: k8s_repo
    stat:
      path: /etc/yum.repos.d/kubernetes.repo
  - name: Write k8s repo
    when: not k8s_repo.stat.exists
    blockinfile:
      create: true
      path: /etc/yum.repos.d/kubernetes.repo
      block: |
        [kubernetes]
        name=Kubernetes
        baseurl=https://packages.cloud.google.com/yum/repos/kubernetes-el7-x86_64
        enabled=1
        gpgcheck=1
        repo_gpgcheck=1
        gpgkey=https://packages.cloud.google.com/yum/doc/yum-key.gpg https://packages.cloud.google.com/yum/doc/rpm-package-key.gpg
  - name: Set SELinux in permissive mode
    selinux:
      policy: targeted
      state: permissive
  - name: Install k8s
    yum:
      name: kubelet,kubeadm,kubectl
      state: latest
      disable_excludes: kubernetes
  - name: Enable and start kubelet
    service:
      name: kubelet
      enabled: true
      state: started
  - name: Turn net.bridge.bridge-nf-call-iptables on
    sysctl:
      name: net.bridge.bridge-nf-call-iptables
      value: '1'
  - name: Turn net.bridge.bridge-nf-call-ip6tables on
    sysctl:
      name: net.bridge.bridge-nf-call-ip6tables
      value: '1'
  - name: Remove swapfile from /etc/fstab
    mount:
      name: swap
      fstype: swap
      state: absent
  - name: Disable swap
    command: swapoff -a
    when: ansible_swaptotal_mb > 0

# Cluster initialization

- hosts: k8s_master
  become: true
  remote_user: ansible
  tasks:
  - name: Initialize cluster (Flannel)
    command: 
      cmd: kubeadm init --pod-network-cidr=10.244.0.0/16
      creates: /etc/kubernetes/admin.conf
    notify: kubernetes initialized
  - name: Export KUBECONFIG environment variable
    lineinfile:
      path: /etc/environment
      line: export KUBECONFIG=/etc/kubernetes/admin.conf
  handlers:
  - name: Initialize Flannel
    command: kubectl apply -f https://raw.githubusercontent.com/coreos/flannel/2140ac876ef134e0ed5af15c65e414cf26827915/Documentation/kube-flannel.yml
    listen: kubernetes initialized
  - name: Save `kubeadm join` command
    command: kubeadm token create --print-join-command
    register: kubeadm_join
    listen: kubernetes initialized

# Nodes' joining

- hosts: k8s_workers
  become: true
  remote_user: ansible
  tasks:
  - name: Join the cluster
    command: 
      cmd: "{{ hostvars.k8s_master.kubeadm_join.stdout }}"
      creates: /etc/kubernetes/kubelet.conf