Solving the AnsibleUndefined Issue When Parsing JSON for Metrics in Ansible

Learn how to extract and structure data from nested JSON in Ansible to avoid `undefined` values while creating a table of metrics.
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Resolving AnsibleUndefined Errors When Parsing JSON Data

When working with JSON data in Ansible, it's not uncommon to encounter issues such as AnsibleUndefined values when trying to access specific attributes. One common situation arises when attempting to extract metrics from complex nested JSON structures. In this guide, we’ll explore how to correctly parse JSON content to obtain desired metrics while avoiding undefined values.

The Problem: Undefined Values in JSON Parsing

In your situation, you have complex JSON data containing nested attributes, and your goal is to extract metrics2 and metrics3 to present them in a tabular format.

You found that when trying to parse metrics2, Ansible returns undefined values like this:

[[See Video to Reveal this Text or Code Snippet]]

This likely stems from incorrect mapping through the nested structure in your JSON. Let's take a closer look at the correct approach to avoid this issue.

Understanding the JSON Structure

Your registered JSON content looks like this:

[[See Video to Reveal this Text or Code Snippet]]

Here, params contains multiple arrays, each consisting of objects with various metrics (metrics1, metrics2, metrics3). To retrieve the desired columns accurately, you need to navigate this structure without losing the context of the nested arrays.

The Solution: Extracting Metrics with JSON Query

Instead of using multiple map functions, which can lead to the AnsibleUndefined issue, we can use json_query, a powerful filter for parsing large and nested JSON objects efficiently.

Here’s how to implement it:

Define Your Variable:
First, ensure your JSON content is structured properly when defining your variables.

[[See Video to Reveal this Text or Code Snippet]]

Use JSON Query to Parse:
To create a table with metrics2 in column 1 and metrics3 in column 2, you can use the following command:

[[See Video to Reveal this Text or Code Snippet]]

This command specifies that you want to extract both metrics2 and metrics3 from each object in the nested structure.

Example Output

When implemented correctly, your output will look like this:

[[See Video to Reveal this Text or Code Snippet]]

Complete Playbook Example

Here's an entire Ansible playbook example demonstrating the above solution:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

Parsing complex JSON can be challenging, but with the right tools and techniques, you can extract meaningful data without running into errors like AnsibleUndefined. By utilizing the json_query function, you can effectively transform nested JSON attributes into structured tables. Following this guide should help you retrieve and display your metrics accurately.

If you have any questions or further issues, feel free to ask in the comments below!