First basic playbook on Ansible is there a better way?

Question

Just getting my head around Ansible. Just trying to see what I am doing wrong or what is a better way to reach my goal.

Task :

My goal here is to update a file /proc/sys/vm/overcommit_memory. I want to put the value 0 into it. I also want the value it was before I changed it to be logged and displayed to me in output in case I need to rollback.

The below works fine but wanted to see if there are better ways to do it.

---
- hosts: "{{ target }}"
  gather_facts: yes
  become: yes

  tasks:

  - name: "update overcommit value on {{ target }} ..."
    shell: |
      echo "the value was "
      cat /proc/sys/vm/overcommit_memory
      echo 0 > /proc/sys/vm/overcommit_memory
      echo "the value now is  "
      cat /proc/sys/vm/overcommit_memory
    register: rc
    become: true
    become_user: root

  - debug:
      var: rc.stdout_lines

Thanks in advance

Answer 1

Regarding your example it is recommend to use an Ansible module, sysctl.

---
- hosts: localhost
  become: true
  gather_facts: true

  vars:

    OVERCOMMIT_MEMORY: 0

  tasks:

  - name: 
    sysctl:
      name: vm.overcommit_memory
      value: "{{ OVERCOMMIT_MEMORY }}"
      state: present

Since Ansible is a Configuration Management it makes sure that the above task is idempotent and the value is available and set after. An "reporting" could than just be like

- name: Show value
  debug:
    msg: "'vm.overcommit_memory' values is {{ OVERCOMMIT_MEMORY }}"

Because of

Ansible lets you define when a particular task has “changed” a remote node using the changed_when conditional. This lets you determine, based on return codes or output, whether a change should be reported in Ansible statistics and whether a handler should be triggered or not.

you will get already the information if the key was there and the value not 0 if.

I also want the value it was before I changed it to be logged and displayed to me in output in case I need to rollback.

For a simple reporting of the current value set you could use a reporting task like

- name: Gather Facts OVERCOMMIT_MEMORY
  shell: "cat /proc/sys/vm/overcommit_memory"
  register: overcommit_memory
  changed_when: false
  failed_when: overcommit_memory.rc != 0 and overcommit_memory.rc != 1

- name: Show vaule
  debug:
    msg: "'vm.overcommit_memory' values was {{ overcommit_memory.stdout }}"

You may need to adjust Defining failure to catch cases if the key and therefore the file does not exists or if access rights are missing.

Further Documentation

• Configuring System Memory Capacity

Since it might be that Ansible facts are already contain the value

• Gathers facts about remote hosts
• Discovering variables: facts and magic variables