Correct way to create dynamic lists in Ansible

Question

I'm looking for advice. I have the following code that creates a list dynamically that I can then later use in a template.

This is a copy of the test code I put together - for the actual role I just added the admins|regex_replace variable into the j2 template.

    ---

  - hosts: localhost
    gather_facts: false

    vars:
      # define empty admins var first so ansible doesn't complain
      admins:

      admin_accounts:
      - name: john
        uid: 1000
        group: sysadmin
        shell: /bin/bash
        comment: "Unix Administrator"
      - name: paul
        uid: 1001
        group: sysadmin
        shell: /bin/bash
        comment: "Unix Administrator"
      - name: george
        uid: 1002
        group: sysadmin
        shell: /bin/bash
        comment: "Unix Administrator"
      - name: ringo
        uid: 1003
        group: sysadmin
        shell: /bin/bash
        comment: "Unix Administrator"

    tasks:

      - name: build array of admin user names
        set_fact: admins="{{ admins}} {{ item.name }}"
        with_items: "{{ admin_accounts }}"

      # print out the fact piping through two jinja2 filters
      # careful with word wrapping
      - debug: msg={{ admins | regex_replace( '\s+',', ' ) | regex_replace`(',\s(.*)','\\1') }}`

This gives me the following:

    PLAY [localhost] ***************************************************************

TASK [build array of admin user names] *****************************************
ok: [localhost] => (item={u'comment': u'Unix Administrator', u'shell': u'/bin/bash', u'group': u'sysadmin', u'name': u'john', u'uid': 1000})
ok: [localhost] => (item={u'comment': u'Unix Administrator', u'shell': u'/bin/bash', u'group': u'sysadmin', u'name': u'paul', u'uid': 1001})
ok: [localhost] => (item={u'comment': u'Unix Administrator', u'shell': u'/bin/bash', u'group': u'sysadmin', u'name': u'george', u'uid': 1002})
ok: [localhost] => (item={u'comment': u'Unix Administrator', u'shell': u'/bin/bash', u'group': u'sysadmin', u'name': u'ringo', u'uid': 1003})

TASK [debug] *******************************************************************
ok: [localhost] => {
    "msg": "john, paul, george, ringo"
}

PLAY RECAP *********************************************************************
localhost                  : ok=2    changed=0    unreachable=0    failed=0

So...I get what I need, but am I going about it the right way?

Ansible version is 2.0.2.0 running on Centos 7.2.

Thanks in advance.

---

Edit: The resultant filter ended up looking like this:

  - name: build list of admin user names
    set_fact:
      admin_list: "{{ admin_accounts | selectattr('state', 'equalto', 'present') | map(attribute='name') | join(', ') }}"
  - debug: msg={{ admin_list }}

Having added another parameter to the yaml:

state: absent

Ringo was left out, as desired.

Answer 1

Filters will operate on lists, so the with_items is really wasteful, and the regex stuff is pretty obtuse for what you're doing. Do you really want a comma-separated string, or do you just want a list of the usernames extracted from the admin_accounts list?

If you just want the list, why not:

set_fact:
  admin_usernames: "{{ admin_accounts | map(attribute='name') | list }}"

... and if you really want the comma-separated list as a flat string, just add a join filter:

set_fact:
  admin_usernames: "{{ admin_accounts | map(attribute='name') | join(', ') }}"

If your ultimate target is a template, though, I'd suggest doing this inside the template, since this looks pretty formatting-related as opposed to logic-related (unless you're just simplifying for Stack Overflow purposes)...

Answer 2

When there is a need to add both prefix and suffix (and making everything a list), look at:

  set_fact:
    extended_etcd_endpoints_list: "{{ groups['etcd'] | map('extract', hostvars, ['ansible_default_ipv4','address']) | map('regex_replace', '^(.*)$','https://\\1:2379') | list  }}"

What is does: takes the list of all machines in the group etcd, extracts the ipv4 address, adds a prefix of 'https://' and a suffix of ':2379'. At the end, everything is transformed to a list.