Ansible Dynamic Inventory

Bonus: Beyond the Blueprint / Guide 41 of 45 / Advanced

• OSUbuntu 26.04 LTS
• ansible-core2.20.1
• Python3.14.4
• TimeAbout 16 min

Ansible accepts three kinds of inventory source: a file, a directory (all sources merged, in filename order), and an executable that prints JSON. The executable must answer --list and --host <name>, though a _meta key containing all hostvars means --host is never actually called - which is why every practical implementation includes it.

This guide includes

Use this when a static inventory file has stopped being maintainable. This matters because an inventory can be a program - it has to answer two specific questions, and the constructed plugin adds groups without you writing any code.

• writing an inventory that is a program rather than a file
• confirming Ansible reads it in exactly the same way
• answering the two questions any inventory script has to answer
• using the constructed plugin to add groups with no code at all
• finding that the key must be a string, and why it cannot group on facts

Before you start

• A control node configured as shown in the first step.
• The session writes ~/dyn-inventory.py and an ~/inv/ directory, and removes both.

1. 1

   The configuration this guide assumes

2. 2

   An inventory that is a program

3. 3

   Ansible reads it the same way

4. 4

   The two questions a script must answer

5. 5

   The constructed plugin adds groups without code

6. 6

   The key must be a string

7. 7

   Why it cannot group on facts

Official sources

• Developing dynamic inventory
• ansible.builtin.constructed
• Working with dynamic inventory