Boot Process

Managing the Boot Process

Managing the boot process with Ansible is a bit disappointing because Ansible offers no specific modules to do so. As a result, you must use generic modules instead, like the file module to manage the systemd boot targets or the lineinfile module to manage the GRUB configuration. What Ansible does offer, however, is the reboot module, which enables you to reboot a host and pick up after the reboot at the exact same location. The next two sections describe how to do this.

Managing Systemd Targets

Managing the default target that a host should start in is a common task on Ansible. However, the systemd module has no options to manage this setting, and no other option to manage it is available. For that reason, you must fall back to a generic option instead.

If you need to manage the default systemd target, a file with the name /etc/systemd/system/default.target has to exist as a symbolic link to the desired default target. See, for instance, Listing 14-5, where the output of the Linux ls -l command is used to show the current configuration.

Listing 14-5 Showing the Default Systemd Target

::: pre_1 [ansible@control rhce8-book]$ ls -l /etc/systemd/system/default.target lrwxrwxrwx. 1 root root 37 Mar 23 05:33 /etc/systemd/system/default.target -> /lib/systemd/system/multi-user.target :::

Because Ansible itself doesn’t have any module to specifically set the default.target, you must use a generic module. In theory, you could use either the command module or the file module, but because the file module is a more specific module to generate the symbolic link, you should use the file module. Listing 14-6 shows how to manage the boot target.

Listing 14-6 Managing the Default Boot Target

::: pre_1 — - name: set default boot target hosts: ansible2 tasks: - name: set boot target to graphical file: src: /usr/lib/systemd/system/graphical.target dest: /etc/systemd/system/default.target state: link :::

Rebooting Managed Hosts

In some cases, a managed host needs to be rebooted while running a playbook. To do so, you can use the reboot module. This module uses several arguments to restart managed nodes. To verify the renewed availability of the managed hosts, you need to specify the test_command argument. This argument specifies an arbitrary command that Ansible should run successfully on the managed hosts after the reboot. The success of this command indicates that the rebooted host is available again.

Equally useful while using the reboot module are the arguments that relate to timeouts. The reboot module uses no fewer than four of them:

• connect_timeout: The maximum seconds to wait for a successful connection before trying again

• post_reboot_delay: The number of seconds to wait after the reboot command before trying to validate the managed host is available again

• pre_reboot_delay: The number of seconds to wait before actually issuing the reboot

• reboot_timeout: The maximum seconds to wait for the rebooted machine to respond to the test command

When the rebooted host is back, the current playbook continues its tasks. This scenario is shown in the example in Listing 14-7, where first all managed hosts are rebooted, and after a successful reboot is issued, the message “successfully rebooted” is shown. Listing 14-8 shows the result of running this playbook. In Exercise 14-2 you can practice rebooting hosts using the reboot module.

Listing 14-7 Rebooting Managed Hosts

::: pre_1 — - name: reboot all hosts hosts: all gather_facts: no tasks: - name: reboot hosts reboot: msg: reboot initiated by Ansible test_command: whoami - name: print message to show host is back debug: msg: successfully rebooted :::

Listing 14-8 Verifying the Success of the reboot Module

::: pre_1 [ansible@control rhce8-book]$ ansible-playbook listing147.yaml

PLAY [reboot all hosts] *************************************************************************************************

TASK [reboot hosts] *****************************************************************************************************
changed: [ansible2]
changed: [ansible1]
changed: [ansible3]
changed: [ansible4]
changed: [ansible5]

TASK [print message to show host is back] *******************************************************************************
ok: [ansible1] => {
    "msg": "successfully rebooted"
}
ok: [ansible2] => {
    "msg": "successfully rebooted"
}
ok: [ansible3] => {
    "msg": "successfully rebooted"
}
ok: [ansible4] => {
    "msg": "successfully rebooted"
}
ok: [ansible5] => {
    "msg": "successfully rebooted"
}

PLAY RECAP **************************************************************************************************************
ansible1                   : ok=2    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0
ansible2                   : ok=2    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0
ansible3                   : ok=2    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0
ansible4                   : ok=2    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0
ansible5                   : ok=2    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

:::

::: box Exercise 14-2 Managing Boot State

1. As a preparation for this playbook, so that it actually changes the default boot target on the managed host, use ansible ansible2 -m file -a “state=link src=/usr/lib/systemd/system/graphical.target dest=/etc/systemd/system/default.target”.

2. Use your editor to create the file exercise142.yaml and write the following playbook header:

---
- name: set default boot target and reboot
  hosts: ansible2
  tasks:

3. Now you set the default boot target to multi-user.target. Add the following task to do so:

- name: set default boot target
  file:
    src: /usr/lib/systemd/system/multi-user.target
    dest: /etc/systemd/system/default.target
    state: link

4. Complete the playbook to reboot the managed hosts by including the following tasks:

- name: reboot hosts
  reboot:
    msg: reboot initiated by Ansible
    test_command: whoami
- name: print message to show host is back
  debug:
    msg: successfully rebooted

5. Run the playbook by using ansible-playbook exercise142.yaml.

6. Test that the reboot was issued successfully by using ansible ansible2 -a “systemctl get-default”. :::