Ansible: How to get a subelement of a nested list of dictionaries

Question

I'd like to build our DNS zones via Ansible. The user should just maintain one variable for the forward-lookup zones (e.g. foo.bar). Reverse-lookup zones (0.0.10.in-appr.arpa) should be auto-generated with Ansible.

The forward-lookup zone variable should look like

dns_zone_config:
    - name: "internal.foo.bar"
      acl:
        - 10.180.0.0/24
        - 10.180.8.0/24
      hosts:
        - name: "fileshare"
          ip: 10.180.0.200
    - name: "infra.foo.bar"
      acl:
        - acl-intern
      hosts:
        - name: "testhost1"
          ip: 11.180.0.100
          no_ptr_record: true
        - name: "testhost2"
          ipv6: fe80::1
        - name: "testhost3"
          ip: 11.180.0.200
    - name: "mx.foo.bar"
      mx:
        - name: "xxxx"
          priority: xxxx
          target: xxxx

dns_zone_config is a list of dictionaries that may contains a key called "hosts" which is again a list of dictionaries.

My current way looks like:

- name: Collect all networks
  include_tasks: 01-networks.yml
  loop: "{{ dns_zone_config }}"
  when: item_dns_zone_config.hosts is defined
  loop_control:
    loop_var: item_dns_zone_config

#from 01-networks.yml
- name: Determine IPv4 networks
  set_fact:
    ipv4_networks: "{{ (ipv4_networks | default([])) + [ item.ip ] }}"
  loop: "{{ item_dns_zone_config.hosts }}"
  when: item.ip is defined and (item.no_ptr_record is not defined or not item.no_ptr_record)

I double loop over dns_zone_config and their host entries. This is very inefficient and slow. I'm pretty sure this can be solve smarter :D

Basically I just need list of all IPs of all zones. I tried json_query() and selectattr() filters but I'm struggling on the fact that not every host entry has IPv4 or IPv6 addresses defined. And I don't want contains IPs if a no_ptr_record: true variable is defined (false or not defined is ok).

From the snippet above the list would only contain: ipv4_networks:

['10.180.0.200','11.180.0.200']

Solution

Figured out how to use json_query properly.

  - debug:                                                                      
      msg: "{{ dns_zone_config | json_query(_query) }}"                         
    vars:                                                                       
      _query: "[].hosts[?!no_ptr_record][].[ip,ipv6][]"    

Results in:

TASK [debug] ***********************************************************************************
ok: [localhost] => {
    "msg": [
        "10.180.0.200",
        "fe80::1",
        "11.180.0.200"
    ]
}

Needs just 1-2 sec instead of ~30 sec with double loops :)

Comments

[simohe]

Could you please explain the query? It looks great. I do not find ? !xx on jmespath.org/tutorial.html#filter-projections (but I probably have found it out now by trying there).

[Mario Nette]

With ? you start a condition check. With ! you can negate a boolean. So [?!no_ptr_record] means take all elements where no_ptr_record is not true. If a list element has not no_ptr_record defined it will be also be handled as false (with negation it will be true). See jmespath.org/specification.html