Working with Ansible facts | Create custom facts with examples

Ansible facts is a term used for system information of the managed nodes. Now the system information could be about OS distribution, release, processor, IP address etc. The task of colleting this remote system information is referred as "Gathering facts" and the collected data or gathered information is referred as facts or variable. We use "setup" module to gather facts from the managed nodes.

There are two types of facts

1. System default facts
2. User defined facts

System default facts

A lot of data in our systems is automatically discovered and made available to Ansible by the managed hosts during the handshake process. This data is very useful and tells us everything about that system, such as:

• The hostname, network interface, and IP address
• The system architecture
• The operating system
• The disk drives
• The processor used and amount of memory
• Whether it is a VM; if yes, is it a virtualization/cloud provider?

You can use "setup" module with ad-hoc commands

[ansible@controller ~]$ ansible server2 -m setup

This will give you a long list of values for server2. You can further add filter with the setup module to only get the required data.

In this example I only wish to get the installed kernel details

[ansible@controller ~]$ ansible server2 -m setup -a 'filter="ansible_kernel"'
server2 | SUCCESS => {
    "ansible_facts": {
        "ansible_kernel": "4.18.0-193.6.3.el8_2.x86_64",
        "discovered_interpreter_python": "/usr/libexec/platform-python"
    },
    "changed": false
}

You can go through the output of -m setup and choose the dictionary keys to use them as filter. For more information on setup module and available filters you can follow official ansible documentation

User defined facts

In this section we will create some user defined facts which can be used by playbooks. This is definitely not mandatory and based on requirement you may choose to create custom facts.

• To create custom facts, we must create /etc/ansible/facts.d on the respective managed nodes
• Inside the facts.d directory you can place your facts file with extension .fact
• The format of these facts file must be in JSON or Dictionary format.
• The fact file must have executable permission

We will use ansible to create the fact script. For the sake of demonstration I will only use server2 but you can use all your managed nodes.

First of all let us create a directory on server2

[ansible@controller ~]$ ansible server2 -m file -a "path=/etc/ansible/facts.d state=directory" --become

Now I will create a fact file locally on my ansible engine which I will copy to the managed nodes using ansible. Following is my fact file /tmp/python_version.fact which will collect the python version:

#!/bin/bash

python_ver=$(python3 --version | cut -d' ' -f2)

cat << EOF
{ "Python_version": "${python_ver}" }
EOF

This script will collect the python version and then print the output in JSON format.

So we will copy this file to server2 using ansible and modify user and group owner to ansible with file permission as 700 so only ansible can access this file.

[ansible@controller ~]$ ansible server2 -m copy -a "src=/tmp/python_version.fact dest=/etc/ansible/facts.d/ mode=700 owner=ansible group=ansible" --become

Verify the file on server2

[ansible@server-2 ~]$ ls -l /etc/ansible/facts.d/python_version.fact
-rwx------ 1 ansible ansible 113 Sep 20 02:49 /etc/ansible/facts.d/python_version.fact

Now we can collect the facts for only this filter

[ansible@controller ~]$ ansible server2 -m setup -a "filter=ansible_local"

Output from my controller node:

What's Next

Next in our Ansible Tutorial we will learn about Ansible Variables and Data Types