使用Ansible中的JINJA2从JSON中提取带有条件的嵌套dict值

Question

I'm trying to extract the CDN domain name for a specific Alias from Ansible's cloudfront_facts , with the following (summarized) output:

{
  "cdn_facts": {
   "ansible_facts": {
    "cloudfront": {
      "summary": {
       "distributions": [
        {
          "Aliases": [
           "media.example.com"
          ],
          "DomainName": "a1b2c3d4e5f6g.cloudfront.net"
        },
        {
          "Aliases": [
           "example.com"
          ],
          "DomainName": "g7f6e5d4c3b2a.cloudfront.net"
        }
      ]
     }
    }
  }
}

In other words, for the Alias example.com I'd like to set a fact with the value of g7f6e5d4c3b2a.cloudfront.net .

I've tried the following to try and print out the value, but it's simply producing an empty list.

- debug:
    msg: "{{ cdn_facts.ansible_facts.cloudfront.summary.distributions | selectattr('Aliases[0]', 'equalto', 'example.com') | map(attribute='DomainName') | list }}"

I'm at a loss on how to even debug this, as cdn_facts.ansible_facts.cloudfront.summary.distributions produces an array of dicts, but selectattr and map are not producing anything.

Answer 1

Nothing in your data has an attribute named Aliases[0] , so that's why your selectattr filter is failing.

For extracting data from deeply nested dictionaries, the json_query filter is often a better choice than trying to chain native Jinja filters. For example, given the alias example.com , the following expression will extract the corresponding DomainName attribute:

cdn_facts.ansible_facts.cloudfront.summary.distributions[?Aliases[0] == `example.com`]|[0].DomainName

We can use that in a playbook like this:

---
- hosts: localhost
  gather_facts: false
  tasks:
    - include_vars:
        file: data.json
        name: data

    - debug:
        msg: >-
          {{ item }} ->
          {{
          (data|json_query('cdn_facts.ansible_facts.cloudfront.summary.distributions[?Aliases[0] == `{}`]|[0].DomainName'.format(item)))
          }}
      loop:
        - media.example.com
        - example.com

Which will output:

TASK [debug] **********************************************************************************************************************************************************************************
ok: [localhost] => (item=media.example.com) => {
    "msg": "media.example.com -> a1b2c3d4e5f6g.cloudfront.net"
}
ok: [localhost] => (item=example.com) => {
    "msg": "example.com -> g7f6e5d4c3b2a.cloudfront.net"
}

The json_query modules uses the jmespath search syntax. You can experiment with jmespath expressions by pasting your data into the text box at https://jmespath.org and then entering search expressions in the field above it. Alternately, you can grab the jpterm command line tool.