Oleksandr Gavenko's blog
2020-10-31 00:00 Experimenting with Ansible connection docker

With some luck you can find official documentation online for Docker integration into Ansible:

https://docs.ansible.com/ansible/latest/plugins/connection.html

Connection Plugins.

https://docs.ansible.com/ansible/latest/scenario_guides/guide_docker.html

Docker Guide.

but I lack of description connection docker. Ansible v2.9 supports connection: docker:

$ ansible-doc -t connection -l | grep docker

docker       Run tasks in docker containers

Documentation suggests to read output of:

$ ansible-doc -t connection docker

Run commands or put/fetch files to an existing docker container.
...

Lets start simple Docker container, install software and remove container afterwards.

We will use localhost as the only inventory host:

- hosts: localhost
  connection: local
  become: false
  gather_facts: no

and dynamically add a Docker managed host after creating it:

tasks:

# https://docs.ansible.com/ansible/latest/collections/community/general/docker_container_module.html
# check that container is running by:
#   docker exec alpine-x ps
- docker_container:
    name: alpine-x
    image: alpine:latest
    # command: sh -c "while sleep 1; do :; done"
    command: tail -f /dev/null
    auto_remove: yes
    cleanup: yes
    oom_killer: yes
    state: started

# https://docs.ansible.com/ansible/latest/collections/ansible/builtin/add_host_module.html
- add_host:
    name: alpine-x
    # To avoid: [WARNING]:
    #   Platform linux on host alpine-x is using the discovered Python interpreter at /usr/bin/python3,
    #   but future installation of another Python interpreter could change this.
    ansible_python_interpreter: /usr/bin/python3

Specail trick command: tail -f /dev/null is used to keep container running infinity.

With module add_host we introduce host dynamically of the same name as Docker container.

According to:

https://docs.ansible.com/ansible/latest/reference_appendices/python_3_support.html

Python 3 Support.

we can define Python interpreter only:

To explicitly configure a Python 3 interpreter, set the ansible_python_interpreter inventory variable at a group or host level to the location of a Python 3 interpreter, such as /usr/bin/python3. The default interpreter path may also be set in ansible.cfg.

That is why we see ansible_python_interpreter in add_host.

On other hand we can avoid setting ansible_connection & ansible_ssh_user:

- add_host:
    name: alpine-x
    ansible_connection: docker
    ansible_ssh_user: root

on add_host level because those settings are supported at plays' hosts settings connection & user:

- hosts: alpine-x
  connection: docker
  user: root
  become: false
  gather_facts: no
  # vars:
  #   ansible_python_interpreter: /usr/bin/python3

  tasks:

  # https://docs.ansible.com/ansible/latest/collections/ansible/builtin/raw_module.html
  - raw:
      apk add python3

  # https://docs.ansible.com/ansible/latest/collections/community/general/apk_module.html
  - apk:
      name: mc
      state: present

Still ansible_python_interpreter could be defined at vars section.

We have to install Python 3 with module row as Alpine images don't have them bundled. Then we can use Ansible modules as usual (apk is an example).

https://wiki.alpinelinux.org/wiki/Ansible

Managed nodes. There are only minimal requirements for the clients. For every system you want to manage, you need to have the client's SSH key in the authorized_keys file of the management system and Python.

https://wiki.alpinelinux.org/wiki/Ansible_APK_Module

Ansible APK Module.

Finally we can destroy running container (remember tail -f /dev/null blocks termination!):

- hosts: localhost
  connection: local
  become: false
  gather_facts: no

  tasks:

  # https://docs.ansible.com/ansible/latest/collections/community/general/docker_container_module.html
  # check that container is stopped:
  #   docker ps
  - docker_container:
      name: alpine-x
      image: alpine:latest
      state: absent

Check full example play-fun-with-docker.yml.

Run it as:

ansible-playbook  play-fun-with-docker.yml

Of cause you need to have Ansible & Docker installed and Docker supervisor running ))

You can communicate with Docker directly (here raw module is used, don't forget to start container $NAME beforehand):

$ id=$(docker run -d --name alpine alpine tail -f /dev/null)

$ ansible all -i "alpine," -c docker -m raw -a 'echo OK'
$ ansible all -i "$id," -c docker -m raw -a 'echo OK'

$ docker stop alpine
$ docker stop $id
ansible

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