Ansible playbook for modifying /etc/docker/daemon.json config (based on https://stackoverflow.com/questions/50796341/add-a-new-key-value-to-a-json-file-using-ansible)

docker-mod.yml

- hosts: all
  become: yes
  gather_facts: false
  vars:

  tasks:
  - name: Check that the /etc/docker/daemon.json exists
    stat:
      path: /etc/docker/daemon.json
    register: stat_result

  - block:
    - name: load var from file
      slurp:
        src: /etc/docker/daemon.json
      register: docker_vars

    - debug:
        msg: "{{ docker_vars.content|b64decode|from_json }}"

    - name: append more key/values
      set_fact:
        docker_vars: "{{ docker_vars.content|b64decode|from_json }}"


    - name: append more key/values
      set_fact:
        docker_vars: "{{ docker_vars | default([]) | combine({ item.key : item.value }) }}"
      with_items:
      - { key: "log-driver", value: "journald" }
      - { key: "registry-mirrors", value: [ "http://registry.dev.local" ] }


    - debug:
        var: docker_vars

    - name: write var to file
      copy:
        content: "{{ docker_vars | to_nice_json }}"
        dest: /etc/docker/daemon.json
    when: stat_result.stat.exists == true