How can I replace DEFAULT_HASH_BEHAVIOR for `group_vars` in Ansible?

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Ansible 2.10.1 provides the following deprecation warning:

[DEPRECATION WARNING]: DEFAULT_HASH_BEHAVIOUR option, This feature is fragile
and not portable, leading to continual confusion and misuse , use the ``combine``
filter explicitly instead. This feature will be removed in version 2.13.

I am currently using this setting to manage how group_vars and host_vars are implicitly merged. So I am wondering how I can do something "explicitly" for an implicit loading of variables? Is there another more specific ansible setting that can be used for this particular merging? Or does this mean that I cannot rely on group_vars and host_vars being implicitly loaded at all, and that I have to explicitly perform the inclusion and merging of those vars myself? Or is there some other way still of achieving non-default hash behavior for ansible's handy autoloading of group_vars?

ansible
1 Answers

Q: "How can I replace DEFAULT_HASH_BEHAVIOR for group_vars in Ansible?"

A: The deprecation warning says: "use the combine filter". The details depend on the use-case. For example, let's have the inventory

shell> cat hosts
[grp001]
srv001

[grp002]
srv002

[grp003]
srv001
srv002

the group_vars

shell> cat group_vars/grp001.yml 
test_var:
    x: grp001
    y: grp001

shell> cat group_vars/grp002.yml 
test_var:
    x: grp002
    z: grp002

shell> cat group_vars/grp003.yml 
test_var:
    x: grp003

and the playbook

shell> cat pb.yml
- hosts: srv001,srv002
  tasks:
    - debug:
        var: test_var

The default behavior is to replace the variables

shell> ansible-playbook pb.yml

ok: [srv001] => {
    "test_var": {
        "x": "grp003"
    }
}
ok: [srv002] => {
    "test_var": {
        "x": "grp003"
    }
}

Optionally, the dictionaries can be merged

shell> ANSIBLE_HASH_BEHAVIOUR=merge ansible-playbook pb.yml

ok: [srv001] => {
    "test_var": {
        "x": "grp003",
        "y": "grp001"
    }
}
ok: [srv002] => {
    "test_var": {
        "x": "grp003",
        "z": "grp002"
    }
}

Without DEFAULT_HASH_BEHAVIOR available (deprecated in 2.13) "use the combine filter". For example, use group_names to include the variables and explicitly combine the dictionaries

shell> cat pb.yml
- hosts: srv001,srv002
  tasks:
    - include_vars:
        file: "group_vars/{{ item }}.yml"
        name: "{{ item }}"
      loop: "{{ group_names }}"
    - set_fact:
        test_var: "{{ test_var|default({})|combine(item) }}"
      loop: "{{ group_names|
                map('extract', hostvars[inventory_hostname], 'test_var')|
                list }}"
    - debug:
        var: test_var

gives

shell> ansible-playbook pb.yml

ok: [srv002] => {
    "test_var": {
        "x": "grp003",
        "z": "grp002"
    }
}
ok: [srv001] => {
    "test_var": {
        "x": "grp003",
        "y": "grp001"
    }
}
References
user_64825610
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