DO374 - ch08s04

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Guided Exercise: Configuring Parallelism

Explore the effects of different serial and forks directives on how Ansible processes a play.

Outcomes

Tune parallel and serial executions of a playbook across multiple managed hosts.

As the student user on the workstation machine, use the lab command to prepare your system for this exercise.

This command ensures that the environment is ready for this exercise.

[student@workstation ~]$ lab start update-parallelism

Procedure 8.2. Instructions

Clone the https://git.lab.example.com/student/update-parallelism.git Git repository to the /home/student/git-repos directory and then create a branch for this exercise.

Create the /home/student/git-repos directory if it does not exist, and then change to this directory.
```
[student@workstation ~]$ mkdir -p ~/git-repos
[student@workstation ~]$ cd ~/git-repos
```

Clone the repository https://git.lab.example.com/student/update-parallelism.git, and then change into the cloned repository:

[student@workstation git-repos]$ git clone \
> https://git.lab.example.com/student/update-parallelism.git
Cloning into 'update-parallelism'...
...output omitted...
[student@workstation git-repos]$ cd update-parallelism

Create the exercise branch.

[student@workstation update-parallelism]$ git checkout -b exercise
Switched to a new branch 'exercise'

Examine the contents of the project directory to become familiar with the project files.

Examine the contents of the ansible.cfg file. Note that the inventory file is set to inventory, the forks parameter is set to 4, and the ansible.posix.timer and ansible.posix.profile_tasks callback plug-ins are enabled.
```
[defaults]
inventory=inventory
remote_user=devops
forks=4
callbacks_enabled=ansible.posix.timer,ansible.posix.profile_tasks
```
Examine the contents of the inventory file. Note that it contains a host group, webservers, that contains four hosts.
```
[webservers]
servera.lab.example.com
serverb.lab.example.com
serverc.lab.example.com
serverd.lab.example.com
```

Examine the contents of the update_httpd.yml playbook. This playbook runs against the webservers host group, ensuring that the latest httpd package is installed and that the httpd service is enabled and started.

---
- name: Update the web server
  hosts: webservers
  become: true
  gather_facts: false

  tasks:
    - name: Latest httpd package installed
      ansible.builtin.yum:
        name: httpd
        state: latest
      notify:
        - Restart httpd

  handlers:
    - name: Restart httpd
      ansible.builtin.service:
        name: httpd
        enabled: true
        state: restarted

Examine the contents of the remove_httpd.yml playbook. This playbook runs against the webservers host group, ensuring that the httpd service is disabled and stopped and that the httpd package is not installed.

---
- name: Remove the web server
  hosts: webservers
  become: true
  gather_facts: false

  tasks:
    - name: Query service facts
      ansible.builtin.service_facts:

    - name: Disable httpd service
      ansible.builtin.service:
        name: httpd
        enabled: false
        state: stopped
      when: ansible_facts['services']['httpd.service'] is defined

    - name: Remove httpd package
      ansible.builtin.yum:
        name: httpd
        state: absent
        autoremove: true

Use the ansible-navigator run command to run the update_httpd.yml playbook.

Watch the playbook as it runs and note how Ansible performs each task on all four hosts at the same time. Also, note the output from the callback plug-ins to determine how long it takes the ansible-navigator command to run the playbook.

[student@workstation update-parallelism]$ ansible-navigator run \
> -m stdout update_httpd.yml

PLAY [Update the web server] ***********************************************

...output omitted...

PLAY RECAP *****************************************************************
servera.lab.example.com    : ok=2    changed=2    unreachable=0    failed=0  ...
serverb.lab.example.com    : ok=2    changed=2    unreachable=0    failed=0  ...
serverc.lab.example.com    : ok=2    changed=2    unreachable=0    failed=0  ...
serverd.lab.example.com    : ok=2    changed=2    unreachable=0    failed=0  ...
Playbook run took 0 days, 0 hours, 0 minutes, 12 seconds
Monday 05 December 2022  20:21:04 +0000 (0:00:01.638)       0:00:12.687 ****
============================================================================
Latest httpd package installed -------------------------------------- 11.02s
Restart httpd -------------------------------------------------------- 1.64s

Run the remove_httpd.yml playbook to stop and disable the httpd service and remove the httpd package.

[student@workstation update-parallelism]$ ansible-navigator run \
> -m stdout remove_httpd.yml
...output omitted...

Change the value of the forks parameter to 1 in the ansible.cfg file, and then time the execution of the update_httpd.yml playbook again.

Change the value of the forks parameter to 1 in the ansible.cfg file.

[defaults]
inventory=inventory
remote_user=devops
forks=1
callbacks_enabled=ansible.posix.timer,ansible.posix.profile_tasks

Run the update_httpd.yml playbook again. Watch the playbook as it runs. This time Ansible performs each task on one host at a time. Notice how decreasing the number of forks causes the playbook execution to take longer.

[student@workstation update-parallelism]$ ansible-navigator run \
> -m stdout update_httpd.yml

PLAY [Update the web server] ***********************************************

...output omitted...

PLAY RECAP *****************************************************************
servera.lab.example.com    : ok=2    changed=2    unreachable=0    failed=0  ...
serverb.lab.example.com    : ok=2    changed=2    unreachable=0    failed=0  ...
serverc.lab.example.com    : ok=2    changed=2    unreachable=0    failed=0  ...
serverd.lab.example.com    : ok=2    changed=2    unreachable=0    failed=0  ...
Playbook run took 0 days, 0 hours, 0 minutes, 23 seconds
Monday 05 December 2022  20:28:31 +0000 (0:00:05.212)       0:00:23.075 ****
============================================================================
Latest httpd package installed -------------------------------------- 17.84s
Restart httpd -------------------------------------------------------- 5.21s

Run the remove_httpd.yml playbook to stop and disable the httpd service and remove the httpd package.

[student@workstation update-parallelism]$ ansible-navigator run \
> -m stdout remove_httpd.yml
...output omitted...

Add the serial parameter to the play in the update_httpd.yml playbooks so that the play only runs on two hosts simultaneously. The beginning of the playbook should consist of the following content:
```
---
- name: Update the web server
  hosts: webservers
  become: true
  gather_facts: false
  serial: 2
```
Set the value of the forks parameter to 2 in the ansible.cfg file. The forks parameter must be at least equal to the value for of the serial parameter; otherwise, it restricts execution speed.
```
[defaults]
inventory=inventory
remote_user=devops
forks=2
callbacks_enabled=ansible.posix.timer,ansible.posix.profile_tasks
```

Run the update_httpd.yml playbook again.

Run the update_httpd.yml playbook again, and watch as it runs. Note that Ansible runs through the entire play on two hosts before rerunning the play on the two remaining hosts.

[student@workstation update-parallelism]$ ansible-navigator run \
> -m stdout update_httpd.yml

PLAY [Update the web server] ***********************************************

TASK [Latest httpd package installed] **************************************
Monday 05 December 2022  20:32:49 +0000 (0:00:00.024)       0:00:00.024 ****
changed: [serverb.lab.example.com]
changed: [servera.lab.example.com]

...output omitted...

PLAY [Update the web server] ***********************************************

TASK [Latest httpd package installed] **************************************
Monday 05 December 2022  20:32:56 +0000 (0:00:01.633)       0:00:06.508 ****
changed: [serverd.lab.example.com]
changed: [serverc.lab.example.com]

...output omitted...

Run the remove_httpd.yml playbook to stop and disable the httpd service and remove the httpd package.

[student@workstation update-parallelism]$ ansible-navigator run \
> -m stdout remove_httpd.yml
...output omitted...

Set the value of the forks parameter back to 4 in the ansible.cfg file.

[defaults]
inventory=inventory
remote_user=devops
forks=4
callbacks_enabled=ansible.posix.timer,ansible.posix.profile_tasks

Set the serial parameter in the update_httpd.yml playbook to 3. The beginning of the playbook should consist of the following content:
```
---
- name: Update the web server
  hosts: webservers
  become: true
  gather_facts: false
  serial: 3
```

Run the update_httpd.yml playbook again, and watch as it runs. Note that Ansible runs through the entire play on three hosts, and then runs the play on the one remaining host.

[student@workstation update-parallelism]$ ansible-navigator run \
> -m stdout update_httpd.yml

PLAY [Update the web server] ***********************************************

TASK [Latest httpd package installed] **************************************
Monday 05 December 2022  20:36:44 +0000 (0:00:00.026)       0:00:00.026 ****
changed: [serverb.lab.example.com]
changed: [servera.lab.example.com]
changed: [serverc.lab.example.com]

...output omitted...

PLAY [Update the web server] ***********************************************

TASK [Latest httpd package installed] **************************************
Monday 05 December 2022  20:36:51 +0000 (0:00:01.666)       0:00:06.753 ****
changed: [serverd.lab.example.com]

...output omitted...

Finish

On the workstation machine, change to the student user home directory and use the lab command to complete this exercise. This step is important to ensure that resources from previous exercises do not impact upcoming exercises.

[student@workstation ~]$ lab finish update-parallelism

This concludes the section.

Discuss Developing Advanced Automation with Red Hat Ansible Automation Platform

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Welcome to the Developing Advanced Automation with Red Hat Ansible Automation (DO374) group!

Deanna

12 wrz 2023

We are excited to launch a space dedicated to the Red Hat Training course Developing Advanced Automation with Red Hat Ansible Automation Platform! To gain the most value from this group - click the "Join Group" button in the upper right hand corner of the group home page.We encourage group members to collaborate in this group to discuss topics, ask questions, share best practices and tips, provide course feedback, and share their accomplishments as it relates to DO374.Read more about Developing Advanced Automation with Red Hat Ansible Automation Platform here.

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Revision: do374-2.2-82dc0d7