How to update nested variables in Ansible

Question

I have some extra information like db connection details etc. stored in /etc/ansible/facts.d/environment.fact.

These are made available as variables like ansible_local.environment.database.name. What is the best way to update the database name?

I tried the set_fact module but could not get it to update the nested variable correctly. It just overwrites the whole ansible_local hash.

- name: Update database name
  set_fact:
  args:
    ansible_local:
      environment:
        database:
          name: "{{ db_name }}"

Answer 1

This should help, assuming you are using Ansible 2.0 or older.

- set_fact:
    test:
      app:
        in: 1
        out: 2

- set_fact:
    test_new:
      app:
        transform: 3

- set_fact:
    test: "{{test|combine(test_new,recursive=True)}}"

- debug: var=test

A combine is a Jinja2 filter included with Ansible. Make sure you are using recursive parameter in such cases.

Answer 2

That's default Ansible behaviour -- override whole hash when changing part of it. See ansible.conf:

# if inventory variables overlap, does the higher precedence one win
# or are hash values merged together?  The default is 'replace' but
# this can also be set to 'merge'.
#hash_behaviour = replace

So if you change it to hash_behaviour = merge it will work as you expect.