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Discover how to create a JSON variable in Ansible that consolidates host details from multiple servers for efficient automation and management.
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How to Create a Combined Variable in Ansible from Multiple Hosts

In the world of automation using Ansible, organizing data effectively is crucial for maintaining coherent configurations across multiple servers. A common scenario arises when you want to combine host details from various machines into a single variable. This consolidated variable can be particularly useful for tasks like modifying the /etc/hosts file on all the servers within a group.

In this post, we will explore how to create a combined variable in Ansible that pulls together hostnames and their corresponding IP addresses from multiple servers.

Scenario Overview

Let’s consider a practical example where you have a set of web servers defined in your Ansible inventory file (inventory.ini):

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You also have a playbook (playbook.yml) ready for execution:

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The goal here is to create a JSON variable var_a that holds the structure like this:

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This variable will be helpful for updating the /etc/hosts file across all web servers.

Solution: Creating the Combined Variable

You can achieve this through the use of the set_fact module in Ansible. Here’s how to do it step-by-step:

Step 1: Define Your Host File

Make sure your host file correctly specifies your servers as shown in the scenario overview. Here's an example host file:

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Step 2: Write the Ansible Task

You'll want to define a task in your playbook to create the combined variable. This uses the set_fact module to gather the necessary details from each host:

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Step 3: Debugging the Output

To confirm that your variable hosts_dict contains the expected values, you can add a debug task:

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Expected Output

When you run the playbook, you should see an output that lists the combined information of your servers:

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Summary

Creating a combined variable in Ansible from multiple hosts is not only possible but can significantly streamline your automation tasks. By utilizing the set_fact module in combination with loops, you can efficiently gather and store information from various servers. This combined variable can then be deployed for further use, such as updating hosts files or configuring services across your infrastructure.

By mastering these techniques, you'll enhance your capabilities in managing larger configurations effectively.