Loops in Ansible Playbook

To demonstrate the 'loop' in Ansible, let's take tasks from a playbook I used in another training to configure a Kubernetes cluster.

---
- name : Install the required packages, set the Selinux to permissive , disable the swap etc 
  hosts: all
  become : True
  tasks :
  
  - name: Ensure SELinux is set to permissive mode in the configuration file 
    lineinfile:
      path: /etc/selinux/config
      regexp: '^SELINUX='
      line: SELINUX=permissive
  
  - name: Put SELinux in permissive mode.
    ansible.posix.selinux:
      policy: targeted
      state: permissive

  - name: Configure required modules
    shell : modprobe overlay ; modprobe br_netfilter

Let's break down the playbook and then enhance the last task to utilize an Ansible loop.

1. Setting SELinux to Permissive Mode:

   • The first two tasks focus on SELinux configuration.

   • In the lineinfile task, we ensure that the SELINUX line in the /etc/selinux/config file is set to permissive.

   • The ansible.posix.selinux task puts SELinux in permissive mode for the targeted policy.

2. Configuring Required Modules:

   • The third task executes a shell command to load two kernel modules: overlay and br_netfilter.

   • These modules are essential for containerization and network filtering.

3. Enhancing the Last Task with an Ansible Loop:

   • Instead of using a shell command directly, let's modify the last task to use an Ansible loop.

   • We'll use the loop keyword to iterate over a list of module names and load them.

   • Here's the updated task:

  - name: Configure required modules using Ansible loop
    shell: "modprobe {{ item }}"
    loop:
      - overlay
      - br_netfilter

• In this new task:

  • The shell module runs the modprobe command for each item in the loop.

  • The item variable represents the current module name (e.g., overlay, br_netfilter).

Now your playbook will dynamically load the specified modules using the Ansible loop!

One other section of the playbook that can be optimized with 'loop' is given below.

  - name: Configure sysctl parameter 
    lineinfile:
      create: yes
      path: /etc/sysctl.d/99-kubernetes-cri.conf
      line: net.bridge.bridge-nf-call-iptables  = 1

  - name: Configure sysctl parameter 
    lineinfile:
      path: /etc/sysctl.d/99-kubernetes-cri.conf
      line: net.ipv4.ip_forward                 = 1

  - name: Configure sysctl parameter 
    lineinfile:
      path: /etc/sysctl.d/99-kubernetes-cri.conf
      line: net.bridge.bridge-nf-call-ip6tables = 1

  - name: Update the change in the configuration 
    shell: sysctl --system

We'll consolidate this into a single task that iterates over the required parameters.

- name: Configure sysctl parameters using Ansible loop
  lineinfile:
    create: yes
    path: /etc/sysctl.d/99-kubernetes-cri.conf
    line: "{{ item }}"
  loop:
    - "net.bridge.bridge-nf-call-iptables = 1"
    - "net.ipv4.ip_forward = 1"
    - "net.bridge.bridge-nf-call-ip6tables = 1"

- name: Update the changes in the configuration
  shell: sysctl --system

In this updated task:

• The lineinfile module will add each parameter line to the specified file.

• The loop iterates over the list of parameters, ensuring cleaner and more concise code.

Here is another instance of 'loop' in the same playbook, which should be self-explanatory. Like this, the playbooks can be simplified and enhanced with appropriate loops.

  - name: Add kubernetes repository
    yum_repository:
      name: Kubernetes
      description: Kubernetes
      baseurl: 'https://pkgs.k8s.io/core:/stable:/v1.28/rpm/'
      #baseurl: https://packages.cloud.google.com/yum/repos/kubernetes-el7-x86_64
      enabled: True
      gpgcheck: False
      gpgcakey : 'https://pkgs.k8s.io/core:/stable:/v1.29/rpm/repodata/repomd.xml.key'
      #gpgkey=https://packages.cloud.google.com/yum/doc/yum-key.gpg https://packages.cloud.google.com/yum/doc/rpm-package-key.gpg
      #exclude: kubelet kubeadm kubectl cri-tools kubernetes-cni

# Kubelet will not start if the system has swap enabled, so let us disable the swap.
  - name: Remove swapfile from /etc/fstab
    mount:
      name: "{{ item }}"
      fstype: swap
      state: absent
    with_items:
      - swap
      - none

  - name: Disable swap
    command: swapoff -a
    when: ansible_swaptotal_mb > 0  

  - name: Install a list of packages for kubernetes
    yum:
      name:
        - kubelet
        - kubeadm
        - kubectl
        - containerd
         
      state: present

Reference

Loops — Ansible Community Documentation.