4.3 Ansible Playbooks - Output

In this lab we learn how to handle output of tasks.

Task 1

Write a playbook output.yml that uses the command module to find all config files of postfix. These files are located under /etc/postfix/ and end with .cf. Targeted server is node1.
Register the result to a variable called output by using the register keyword.
Include a task using the debug module to print out all content of the variable output. If unsure, consult the documentation about the debug module.

Note

You might need to install the postfix package on node1.

Solution Task 1

Documentation about debug module Example output.yml:

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---
- hosts: node1
  become: true
  tasks:
    - name:
      command: "find /etc/postfix -type f -name *.cf"
      register: output
    - debug:
        var: output

Task 2

Add another task to the playbook output.yml using the debug module and print out the resulting filenames of the search above.

Tip

Use an appropriate return value to show the output. Information about return values can be found here: Ansible Docs - Common Return Values

Now, loop over the results and create a backup file called <filename.cf>.bak for each file <filename.cf> that was found. Use the command module. Remember, that the result is probably a list with multiple elements.

Solution Task 2

Example output.yml:

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---
- hosts: node1
  become: true
  tasks:
    - name:
      command: "find /etc/postfix -type f -name *.cf"
      register: output
    - debug:
        var: output.stdout_lines
    - name: create backup
      command: "cp {{ item }} {{ item }}.bak"
      loop: "{{ output.stdout_lines  }}"

Task 3 (Advanced)

Now we enhance our playbook output.yml to only create the backup if no backup file is present.
Solve this task by searching for files ending with .bak and registering the result to a variable. Then do tasks only if certain conditions are met.

Tip

Have a look at the documentation about the command module: Ansible Docs - command

Solution Task 3

Possible solution 1: Example output.yml:

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---
- hosts: node1
  become: true
  tasks:
    - name:
      command: "find /etc/postfix -type f -name *.cf"
      register: output
    - name: create backup only when no backupfile is present
      command: "cp {{ item }} {{ item }}.bak"
      # only do this if there is no .bak for file: item
      args:
        creates: "{{ item }}.bak"
      loop: "{{ output.stdout_lines }}"

Possible solution 2: Example output.yml:

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---
- hosts: node1
  become: true
  tasks:
    - name:
      command: "find /etc/postfix -type f -name *.cf.bak"
      register: search
    - name:
      command: "find /etc/postfix -type f -name *.cf"
      register: output
    - name: create backup only when no backupfile is present
      command: "cp {{ item }} {{ item }}.bak"
      loop: "{{ output.stdout_lines  }}"
      # only do this if there is no .bak for file: item
      when: search.stdout.find(item) == -1

Task 4 (Advanced)

Ensure httpd is stopped on the group web by using an Ansible ad hoc command.
Write a play servicehandler.yml that does the following:
Install httpd by using the dnf module
Start the service httpd with the command module. Don’t use service or systemd module.
Start the service only if it is not started and running already. (The output of systemctl status httpd doesn’t contains the string Active: active (running))

Note

Have a look at the documentation about conditionals: Ansible Docs - Playbook Conditionals

systemctl status returns status failed when a service is not running. Therefore we use ignore_errors: true in the corresponding task to let Ansible continue anyways.

Solution Task 4

Stop the httpd service with Ansible:

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ansible web -b -a "systemctl stop httpd"

Content of servicehandler.yml:

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---
- hosts: web
  become: true
  tasks:
    - name: install httpd
      dnf:
        name: httpd
        state: present
    - name: check state of service httpd
      command: 'systemctl status httpd'
      register: status
      ignore_errors: true
    - debug:
        var: status.stdout
    - name: start httpd
      command: 'systemctl start httpd'
      when: "'Active: active (running)' not in status.stdout"

Task 5 (Advanced)

Rewrite the playbook servicehandler.yml and ensure that the ignore_errors: true line is removed. Instead set the state of the task to failed when and only when the output of systemctl status httpd contains the string “failed”.

Note

Have a look at the documentation about error handling: Ansible Docs - Playbooks Error Handling

Rerun your playbook and ensure it still runs fine.
By using an ansible ad hoc command, place an invalid configuration file /etc/httpd/conf/httpd.conf and backup the file before. Use the copy module to do this in ad hoc command.
Restart httpd by using an Ansible ad hoc command. This should fail since the config file is not valid.
Rerun your playbook and ensure it fails.
Fix the errors in the config file, restart httpd on node1 and rerun your playbook. Everything should be fine again.

Solution Task 5

Example servicehandler.yml:

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---
- hosts: web
  become: true
  tasks:
    - name: install httpd
      dnf:
        name: httpd
        state: present
    - name: check state of service httpd
      command: 'systemctl status httpd'
      register: status
      failed_when: "'failed' in status.stdout"
    - debug:
        var: status.stdout
    - name: start httpd
      command: 'systemctl start httpd'
      when: "'Active: active (running)' not in status.stdout"

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ansible web -b -m copy -a "content='bli bla blup' dest=/etc/httpd/conf/httpd.conf backup=yes"

Now fix your apache config. You could use the backup of the file created in the previous ad-hoc command.

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ansible web -b -m service -a "name=httpd state=restarted"

All done?

Output as YAML instead of JSON

Last modified November 20, 2023: Merge pull request #216 from puzzle/psc_edaserver_lab (d791dbe)