Extracting Specific Key-Value Pairs from a List of Dictionaries in Ansible

Have you ever encountered a situation in Ansible where you had a list of dictionaries, each representing an item with multiple attributes, and you needed to extract only specific key-value pairs while keeping the rest of the data hidden? Such as wanting to specific data from a list of dictionaries that contains secrets that you did not want logged in Ansible stdout or stderr, but also did not to use no_log, making troubleshooting difficult? This can be a common requirement when working with sensitive information or when you want to streamline the data passed to a task. In this article, we’ll explore how to solve this problem in Ansible, leveraging powerful filters and techniques to extract specific key-value pairs from a list of dictionaries.

Let’s dive into an example playbook that demonstrates the solution. Suppose we have a list called my_list with dictionaries representing individuals, and we want to extract the name and age key-value pairs for each person while keeping the other attributes hidden. Here’s how we can achieve that:

- name: Extract name and age using json_query 
  hosts: localhost
  gather_facts: false
  vars:
    my_list:
      - name: John
        age: 25
        country: USA
      - name: Alice
        age: 30
        country: UK
      - name: Bob
        age: 35
        country: Australia
  tasks:
    - name: Extract name-age pair from each item
      debug:
        msg: "{{ my_list | json_query('[].{name: name, age: age}') }}"

In this example, we use the json_query filter with the JMESPath query [].{name: name, age: age}. This query instructs Ansible to iterate over each element in the my_list variable and create a new dictionary with the keys name and age, using the corresponding values from each dictionary in the original list.

When running this playbook, the output will only include the extracted name-age pairs, while the other data in the dictionaries remains hidden:

TASK [Extract name and age using json_query] ***********************************
ok: [localhost] => {
    "msg": [
        {
            "age": 25,
            "name": "John"
        },
        {
            "age": 30,
            "name": "Alice"
        },
        {
            "age": 35,
            "name": "Bob"
        }
    ]
}

By following this approach, you can easily extract specific key-value pairs from a list of dictionaries in Ansible without exposing the remaining data. This provides a clean and secure way to pass only the necessary information to tasks, ensuring privacy and efficiency in your automation workflows.