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ass="hljs-strong">* ok: [demo.example.com] => { "msg": "harmful task" } ok: [demo2.example.com] => { "msg": "harmful task" }</pre></div><div id="c415"><pre>PLAY RECAP **************************************************************************************** demo.example.com : ok=2 changed=0 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0
demo2.example.com : ok=2 changed=0 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0</pre></div><div id="b2db"><pre>ansible-pilot $</pre></div><h1 id="595a">Ansible Playbook hosts</h1><ul><li>`<code>hosts: HOSTNAME</code>`</li><li>`<code>ansible-playbook PLAYBOOK</code>`</li></ul>Using the `<code>hosts</code>` statement in the Ansible Playbook allows you to specify a host or a group of hosts for the execution. The advantage is that is more reliable than manually specifying the hostname than using the `<code>--limit</code>` parameter from the command line. The drawback is that you need to remember to edit the Ansible Playbook code every time. If you don’t you’re going to execute the code on the specified host, still a potential manual issue.<h2 id="de8c">code</h2><ul><li>playbook2.yml</li></ul><div id="de3a"><pre>--- - name: harmful playbook hosts: demo.example.com tasks: - name: harmful task ansible.builtin.debug: msg: "harmful task"</pre></div><h2 id="a555">execution</h2><div id="28c7"><pre>ansible-pilot$ ansible-playbook -i limit/inventory limit/playbook2.yml</pre></div><div id="6f88"><pre>PLAY [harmful playbook] </pre></div><div id="27a9"><pre>TASK [Gathering Facts] ****************** ok: [demo.example.com]</pre></div><div id="c864"><pre>TASK [harmful task] ****************** ok: [demo.example.com] => { "msg": "harmful task" }</pre></div><div id="ce46"><pre>PLAY RECAP  demo.example.com : ok=2 changed=0 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0</pre></div><div id="1ac1"><pre>ansible-pilot $</pre></div><h1 id="acbe">Ansible Playbook hosts advanced</h1><ul><li>`<code>hosts: “{{ HOSTS }}”</code>`</li><li>`<code>ansible-playbook -e “HOSTS=demo.example.com” PLAYBOOK</code>`</li></ul>Using the `<code>hosts</code>` statement in the Ansible Playbook allows you to specify also a variable that you could populate with a host or a group of host for the execution. Basically, if you blindly execute the Ansible Playbook code on the command line is doing nothing. The only way is to process is to populate the host variable via an extra variable via the console line. The advantage is that is more reliable than manually specifying the hostname than using the `<code>--limit</code>` parameter from the command line. This option combines the advantages of the previous option and my favorite as well.<h2 id="c797">code</h2><ul><li>playbook3.yml</li></ul><div id="73ec"><pre>--- - name: harmful playbook hosts: "{{ HOSTS }}" tasks: - name: harmful task ansible.builtin.debug: msg: "harmful task"</pre></div><h2 id="ca0d">execution</h2><div id="80ca"><pre>ansible-pilot$ ansible-playbook -i limit/inventory -e "HOSTS=demo.example.com" limit/playbook3.yml</pre></div><div id="ffda"><pre>PLAY [harmful playbook] </pre></div><div id="1b1d"><pre>TASK [Gathering Facts] ***<span class="hljs-s

Options

trong"> ok: [demo.example.com]</pre></div><div id="66ac"><pre>TASK [harmful task] * ok: [demo.example.com] => { "msg": "harmful task" }</pre></div><div id="d3ca"><pre>PLAY RECAP  demo.example.com : ok=2 changed=0 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0</pre></div><div id="4a0e"><pre>ansible-pilot $</pre></div><h2 id="58f9">wrong execution</h2><div id="6bab"><pre>ansible-pilot$ ansible-playbook -i limit/inventory limit/playbook3.yml [WARNING]: Could not match supplied host pattern, ignoring: HOSTS</pre></div><div id="cbbe"><pre>PLAY [harmful playbook] * skipping: no hosts matched</pre></div><div id="c824"><pre>PLAY RECAP </pre></div><div id="709b"><pre>ansible-pilot $</pre></div><h1 id="896f">Recap</h1>Now you know the Three options to Safely Limit Ansible Playbooks Execution to a Single Machine that you could apply to your everyday journey based on your use case.Subscribe to the<a href="https://www.youtube.com/channel/UC5MNbTYRHSCu9vAki3z9SmA"> YouTube channel</a>,<a href="https://ansiblepilot.medium.com/"> Medium</a>, and<a href="https://www.ansiblepilot.com/"> Website</a> to not miss the next episode of the Ansible Pilot.<h2 id="7fd8">Video Course</h2><ul><li><a href="https://click.linksynergy.com/deeplink?id=euGmLrdj*Ec&mid=39197&murl=https%3A%2F%2Fwww.udemy.com%2Fcourse%2Fansible-by-examples-devops%2F%3FreferralCode%3D8E065F6D6F8622A3DEC8">Learn Ansible Automation in 250+examples & practical lessons: Learn Ansible with some real-life examples of how to use the most common modules and Ansible Playbook</a></li></ul><h2 id="a033">Printed Book</h2><figure id="7621"><img src="https://cdn-images-1.readmedium.com/v2/resize:fit:800/0*eK7ZTcUkiSDTh6S7"><figcaption><a href="https://amzn.to/3XHeDLd">Ansible for VMware by Examples</a></figcaption></figure><figure id="b595"><img src="https://cdn-images-1.readmedium.com/v2/resize:fit:800/0*ct4RPFWWWeUP1m9S"><figcaption><a href="https://amzn.to/3NLCAMB">Ansible for Kubernetes by Example</a></figcaption></figure><figure id="4719"><img src="https://cdn-images-1.readmedium.com/v2/resize:fit:800/0*hvcRcNX06JcnqTTK"><figcaption><a href="https://amzn.to/43HEMuL">Hands-on Anasible Automation</a></figcaption></figure><h2 id="223c">eBooks</h2><ul><li><a href="https://leanpub.com/ansiblebyexamples">Ansible by Examples: 200+ Automation Examples For Linux and Windows System Administrator and DevOps</a></li><li><a href="https://leanpub.com/ansibleforwindowsbyexamples">Ansible For Windows By Examples: 50+ Automation Examples For Windows System Administrator And DevOps</a></li><li><a href="https://leanpub.com/ansibleforlinuxbyexamples">Ansible For Linux by Examples: 100+ Automation Examples For Linux System Administrator and DevOps</a></li><li><a href="https://leanpub.com/linuxfileanddirectorybyansibleexamples">Ansible Linux Filesystem By Examples: 40+ Automation Examples on Linux File and Directory Operation for Modern IT Infrastructure</a></li><li><a href="https://leanpub.com/ansible-for-kubernetes-by-examples">Ansible For Containers and Kubernetes By Examples: 20+ Automation Examples To Automate Containers, Kubernetes and OpenShift</a></li><li><a href="https://leanpub.com/ansibleforsecuritybyexamples">Ansible For Security by Examples: 100+ Automation Examples to Automate Security and Verify Compliance for IT Modern Infrastructure</a></li><li><a href="https://leanpub.com/ansible-tips-and-tricks">Ansible Tips and Tricks: 10+ Ansible Examples to Save Time and Automate More Tasks</a></li><li><a href="https://leanpub.com/ansiblelinuxusersandgroupsbyexamples">Ansible Linux Users & Groups By Examples: 20+ Automation Examples on Linux Users and Groups Operation for Modern IT Infrastructure</a></li><li><a href="https://leanpub.com/ansible-for-postgresql-by-examples">Ansible For PostgreSQL by Examples: 10+ Examples To Automate Your PostgreSQL Database</a></li><li><a href="https://leanpub.com/ansible-for-aws-by-examples">Ansible For Amazon Web Services AWS By Examples: 10+ Examples To Automate Your AWS Modern Infrastructure</a></li><li><a href="https://leanpub.com/Ansible-Automation-Platform/">Ansible Automation Platform By Example: A step-by-step guide for the most common user scenarios</a></li></ul><h1 id="3063">Donate</h1><div id="c671" class="link-block"> <a href="https://patreon.com/lucaberton"> <div> <div> <h2>Luca Berton is creating Software Open Source for Ansible | Patreon</h2> <div><h3>Become a patron of Luca Berton today: Get access to exclusive content and experiences on the world's largest membership…</h3></div> <div>patreon.com</div> </div> <div> <div style="background-image: url(https://miro.readmedium.com/v2/resize:fit:320/0*YpFcQ4mmKi09is62)"></div> </div> </div> </a> </div><div id="c681" class="link-block"> <a href="https://github.com/sponsors/lucab85"> <div> <div> <h2>Sponsor @lucab85 on GitHub Sponsors</h2> <div><h3>I am an active Open Source contributor, involved in Ansible communities, though I am all over the place. @lucab85's…</h3></div> <div>github.com</div> </div> <div> <div style="background-image: url(https://miro.readmedium.com/v2/resize:fit:320/0*VNJTrIi-0nHm1mC1)"></div> </div> </div> </a> </div><figure id="56d7"><img src="https://cdn-images-1.readmedium.com/v2/resize:fit:800/1*qGzstR1pOn6sqYsO3Vxakg.png"><figcaption></figcaption></figure></article></body>

Three options to Safely Limit Ansible Playbooks Execution to a Single Machine

Three options to limit the execution of a potentially harmful Ansible Playbook to only one host.

Three options to Safely Limit Ansible Playbooks Execution to a Single Machine.

Today we’re going to talk about the three options to limit the execution of a potentially harmful Ansible Playbook to only one host.

I’m Luca Berton and welcome to today’s episode of Ansible Pilot.

Limit Ansible Playbook to only one HOSTNAME

use `--limit` at runtime
`hosts: HOSTNAME` Ansible Playbook
`hosts: “{{ HOSTS }}”` Ansible Playbook

Let’s deep dive into our use case to Limit Ansible Playbook to only one HOSTNAME.

I’m going to show three different ways to achieve this result:

using the `--limit` parameter at runtime, limit the HOSTNAME in the Playbook code and the most advanced way is to define a variable in the Ansible Playbook that you could populate on-demand.

Let’s discuss the pros and cons of each option.

demo

In the following demo scenarios, I’d like to execute my harmful Ansible Playbook ONLY against demo.example.com host.

This is my demo inventory file:

[linux]
demo.example.com
demo2.example.com

[all:vars]
ansible_connection=ssh
ansible_user=devops
ansible_ssh_private_key_file=~/.ssh/id_rsa

Ansible command limit option

`--limit`
`ansible-playbook — limit HOSTNAME PLAYBOOK`

Using the `--limit` parameter of the `ansible-playbook` command is the easiest option to limit the execution of the code to only one host. The advantage is that you don’t need to edit the Ansible Playbook code before executing to only one host. The drawback is that you should remember every time you execute the command and sometimes humans are not so reliable.

code

playbook.yml

---
- name: harmful playbook
  hosts: all
  tasks:
    - name: harmful task
      ansible.builtin.debug:
        msg: "harmful task"

execution

ansible-pilot $ ansible-playbook --limit demo.example.com -i limit/inventory limit/playbook.yml

PLAY [harmful playbook] ***************************************************************************

TASK [Gathering Facts] ****************************************************************************
ok: [demo.example.com]

TASK [harmful task] *******************************************************************************
ok: [demo.example.com] => {
    "msg": "harmful task"
}

PLAY RECAP ****************************************************************************************
demo.example.com           : ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

ansible-pilot $

wrong execution

If we forgot the --limit option the result could be very harmful.

ansible-pilot $ ansible-playbook -i limit/inventory limit/playbook.yml

PLAY [harmful playbook] ***************************************************************************

TASK [Gathering Facts] ****************************************************************************
ok: [demo.example.com]
ok: [demo2.example.com]

TASK [harmful task] *******************************************************************************
ok: [demo.example.com] => {
    "msg": "harmful task"
}
ok: [demo2.example.com] => {
    "msg": "harmful task"
}

PLAY RECAP ****************************************************************************************
demo.example.com           : ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
demo2.example.com          : ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

ansible-pilot $

Ansible Playbook hosts

`hosts: HOSTNAME`
`ansible-playbook PLAYBOOK`

Using the `hosts` statement in the Ansible Playbook allows you to specify a host or a group of hosts for the execution. The advantage is that is more reliable than manually specifying the hostname than using the `--limit` parameter from the command line. The drawback is that you need to remember to edit the Ansible Playbook code every time. If you don’t you’re going to execute the code on the specified host, still a potential manual issue.

code

playbook2.yml

---
- name: harmful playbook
  hosts: demo.example.com
  tasks:
    - name: harmful task
      ansible.builtin.debug:
        msg: "harmful task"

execution

ansible-pilot $ ansible-playbook -i limit/inventory limit/playbook2.yml

PLAY [harmful playbook] ***************************************************************************

TASK [Gathering Facts] ****************************************************************************
ok: [demo.example.com]

TASK [harmful task] *******************************************************************************
ok: [demo.example.com] => {
    "msg": "harmful task"
}

PLAY RECAP ****************************************************************************************
demo.example.com           : ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

ansible-pilot $

Ansible Playbook hosts advanced

`hosts: “{{ HOSTS }}”`
`ansible-playbook -e “HOSTS=demo.example.com” PLAYBOOK`

Using the `hosts` statement in the Ansible Playbook allows you to specify also a variable that you could populate with a host or a group of host for the execution. Basically, if you blindly execute the Ansible Playbook code on the command line is doing nothing. The only way is to process is to populate the host variable via an extra variable via the console line. The advantage is that is more reliable than manually specifying the hostname than using the `--limit` parameter from the command line. This option combines the advantages of the previous option and my favorite as well.

code

playbook3.yml

---
- name: harmful playbook
  hosts: "{{ HOSTS }}"
  tasks:
    - name: harmful task
      ansible.builtin.debug:
        msg: "harmful task"

execution

ansible-pilot $ ansible-playbook -i limit/inventory -e "HOSTS=demo.example.com" limit/playbook3.yml

PLAY [harmful playbook] ***************************************************************************

TASK [Gathering Facts] ****************************************************************************
ok: [demo.example.com]

TASK [harmful task] *******************************************************************************
ok: [demo.example.com] => {
    "msg": "harmful task"
}

PLAY RECAP ****************************************************************************************
demo.example.com           : ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

ansible-pilot $

wrong execution

ansible-pilot $ ansible-playbook -i limit/inventory limit/playbook3.yml 
[WARNING]: Could not match supplied host pattern, ignoring: HOSTS

PLAY [harmful playbook] ***************************************************************************
skipping: no hosts matched

PLAY RECAP ****************************************************************************************

ansible-pilot $

Recap

Now you know the Three options to Safely Limit Ansible Playbooks Execution to a Single Machine that you could apply to your everyday journey based on your use case.

Subscribe to the YouTube channel, Medium, and Website to not miss the next episode of the Ansible Pilot.

Video Course

Learn Ansible Automation in 250+examples & practical lessons: Learn Ansible with some real-life examples of how to use the most common modules and Ansible Playbook

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