Ansible

Ansible is a tool that allows you to automate some common operations on a set of hosts.

There is separate section for description how to setup sandbox that I’ll use to exeperiment with ansible. Check particular page for detail just use forllowing command to start the ansible sandbox:

docker compose -f ansible/setup_files/compose.yml up -d &> /dev/null

Note don’t forget to down project after all.

docker compose -f ansible/setup_files/compose.yml down --volumes &> /dev/null

Run command

The ansible.builtin.command extension allows you to run commands in the shell of the inventory hosts.

---

As an example, consider the playbook defined in the following cell. This playbook specifies a job that will write some text into the test_file on the control node.

docker exec control_node sh -c  "
cat << EOF > playbook.yaml
- name: Run example
  hosts: myhosts
  tasks:
   - name: Run task
     ansible.builtin.command: echo \"command example\" > test_file
     register: output
"

The next cell shows the execution of the previously created playbook and it’s result in the file that appeared in the corresponding folder.

docker exec -it control_node \
    ansible-playbook -i inventory.ini playbook.yaml &> /dev/null
docker exec managed_node cat test_file

command example

Copy files

You can copy files from master node to managed node by using corresponding “ansible.builtin.copy” module.

---

The following cell creates a playbook that copies itself to the managed node:

docker exec control_node sh -c  "
cat << EOF > playbook.yaml
- name: Copy example
  hosts: myhosts
  tasks:
   - name: Copy task
     ansible.builtin.copy:
       src: ./playbook.yaml
       dest: /hello_secret_file"

Here is what such playbook run looks like:

docker exec control_node ansible-playbook -i inventory.ini playbook.yaml

PLAY [Copy example] ************************************************************

TASK [Gathering Facts] *********************************************************
ok: [managed_node]

TASK [Copy task] ***************************************************************
changed: [managed_node]

PLAY RECAP *********************************************************************
managed_node               : ok=2    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   

As a result, you will find the copied file in the managed node:

docker exec managed_node cat hello_secret_file

- name: Copy example
  hosts: myhosts
  tasks:
   - name: Copy task
     ansible.builtin.copy:
       src: ./playbook.yaml
       dest: /hello_secret_file

Jinja2 templates

You can use jinja2 templates right in your ansible script. Check corresponding page in the official documentation.

---

The following cell adds playbook that prints ‘hi’ or ‘wrong’ in dependence of the value of the environment variable TEMP_VAR.

docker exec control_node sh -c  "
cat << EOF > playbook.yaml
- name: Show
  hosts: myhosts
  tasks:
   - name: show task
     ansible.builtin.debug:
      msg: \"{{ 'hi' if lookup('env', 'TEMP_VAR') == 'hello' else 'wrong' }}\"
"

The following cell plays the book created by specifying export TEMP_VAR=hello before.

docker exec control_node sh -c "
export TEMP_VAR=hello`
ansible-playbook -i inventory.ini playbook.yaml
"

PLAY [Show] ********************************************************************

TASK [Gathering Facts] *********************************************************
ok: [managed_node]

TASK [show task] ***************************************************************
ok: [managed_node] => {
    "msg": "hi"
}

PLAY RECAP *********************************************************************
managed_node               : ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   

So according to the specified logic, we got the message “hi”.

Now do the same run but with TEMP_VAR taking a different value.

docker exec control_node sh -c "
export TEMP_VAR=else
ansible-playbook -i inventory.ini playbook.yaml
"

PLAY [Show] ********************************************************************

TASK [Gathering Facts] *********************************************************
ok: [managed_node]

TASK [show task] ***************************************************************
ok: [managed_node] => {
    "msg": "wrong"
}

PLAY RECAP *********************************************************************
managed_node               : ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0