📋

Ansible Inventory & Ad-Hoc Commands

Tell Ansible which servers to manage, then run instant commands across all of them.

⏱12 min read📚DevOps Fundamentals

Before Ansible can configure servers, it needs to know they exist. That’s the inventory. Once it does, ad-hoc commands let you run a single action across every server instantly — perfect for quick checks before you write full playbooks.

🎯 Learning Objectives

By the end of this lesson you will:

Write an inventory file and organize hosts into groups
Test connectivity with the ping module
Run ad-hoc commands across servers
Understand when to use ad-hoc vs a playbook

The Inventory File

An inventory lists your managed nodes, optionally grouped. Here’s a simple inventory.ini:

ini

[web]
web-01 ansible_host=203.0.113.10
web-02 ansible_host=203.0.113.11

[db]
db-01 ansible_host=203.0.113.20

[all:vars]
ansible_user=ubuntu

[web] and [db] are groups — you can target a whole group at once.
[all:vars] sets variables (like the SSH user) for every host.

💡 Groups are how you target servers

Grouping lets you say “run this on all web servers” or “only the database”. Real inventories group by role (web/db/cache), environment (prod/staging), or region.

Test Connectivity: the ping Module

The first thing to run against any new inventory — it confirms Ansible can reach and authenticate to each host:

bash

ansible all -i inventory.ini -m ping

bash — 80×24

student@devops:~$ansible web -i inventory.ini -m ping

web-01 | SUCCESS => {
  "changed": false,
  "ping": "pong"
}
web-02 | SUCCESS => {
  "changed": false,
  "ping": "pong"
}

⚠ Ansible ping is not ICMP

The ping module doesn’t send network pings — it connects over SSH and checks Python is usable on the target. A SUCCESS ... "pong" means the whole connection + auth path works.

Ad-Hoc Commands

An ad-hoc command runs a single module against hosts without writing a playbook. The shape is:

text

ansible <group> -i inventory.ini -m <module> -a "<arguments>"

Some useful examples:

bash

# Check uptime on all web servers
ansible web -i inventory.ini -m command -a "uptime"

# Check disk space everywhere
ansible all -i inventory.ini -m command -a "df -h /"

# Install nginx (needs sudo -> --become)
ansible web -i inventory.ini -m apt -a "name=nginx state=present" --become

💡 --become = sudo

--become tells Ansible to escalate privileges (run as root via sudo) for tasks that need it, like installing packages or editing system files.

Ad-Hoc vs Playbook

Use ad-hoc when…	Use a playbook when…
One quick action (restart, check)	Multiple steps that belong together
Exploring / troubleshooting	You want it repeatable and version-controlled
No need to keep it	It’s part of your standard setup

Ad-hoc is the “quick command” mode; playbooks (next lesson) are the durable, reusable mode.

🧪 Hands-on Lab

📝

Build an Inventory and Ping It

Create inventory.ini with a [web] group containing one or two hosts you can SSH to (or use localhost with ansible_connection=local).
Run the ping module against the group and confirm SUCCESS.
Run an ad-hoc command module to get uptime from the hosts.
Try an ad-hoc command that needs --become.

🧠 Knowledge Check

Knowledge Check

What is the purpose of an Ansible inventory file?

It stores the output of every commandIt lists the managed hosts (and groups) Ansible can targetIt contains the Python code Ansible runsIt is a log of failed connections

Knowledge Check

When is an ad-hoc command the better choice over a playbook?

For a complex multi-step setup you'll reuseFor a quick one-off action like checking uptime or restarting a serviceWhenever you need version controlAd-hoc commands can't target multiple servers

💼 Interview Preparation

Interview Q&A

How do you organize an Ansible inventory for a real environment?

Summary

You can now define an inventory, verify connectivity with ping, and run ad-hoc commands across groups of servers. Next, we capture multi-step configuration as reusable playbooks — the heart of Ansible.

Up Next

Ansible Playbooks

You've mastered this lesson. Continue your journey to becoming a DevOps Engineer.

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